The South Zone of the Ranji Trophy, 1989-90 comprised of 6 teams that mainly hailed from the Southern region of India. The teams were participating in the tournament on a regular basis for the previous several editions and they included the likes of Andhra Pradesh, Goa, Hyderabad, Karnataka, Kerala and Tamil Nadu. The teams first played against each other in the zone with the aim of becoming one of the top two teams in the zone. Then the top two teams of the zone were promoted to the knock out level of the tournament for competing with the top teams of the other zones for the championship title. The teams like Karnataka and Hyderabad became the toppers in the zone with total of 87 and 82 points, respectively and they also entered into the knock out level from the zone.

The match between the teams of Hyderabad and Karnataka was the first of the South Zone league matches in the Ranji Trophy, 1989-90 and the two teams played the match at Secunderabad from 18-20 November, 1989. The Karnataka and Hyderabad teams earned 15 and 13 points respectively from the match as it remained drawn. The teams of Goa and Hyderabad played against each other in the second match of the South Zone that was held at Margao from 25-27 November, 1989. The match saw the Hyderabad team earning 21 points by clinching a victory of an innings and 180 runs and the Goa team also earned 1 point from the match. The Goa team then played against the Andhra team in the third match of the zone and the match took place at Vishakhapatnam from 02-04 December, 1989. The Andhra and Goa teams earned 11 and 8 points, respectively from the drawn match.

The fourth of the South Zone league matches in the Ranji Trophy, 1989-90 involved the teams like Tamil Nadu and Kerala and the match was held at Madras (Chennai) from 02-04 December, 1989. Both the teams played very well in the match and as a result, the match went on to be drawn during the specified period of time. The match officials awarded the Tamil Nadu and Kerala teams 13 and 5 points respectively for the drawn match. The teams of Karnataka and Tamil Nadu played against each other in the next match of the zone which was held at Bangalore from 9-11 December, 1989. The Tamil Nadu and Kerala teams earned 13 and 7 points respectively from the drawn match. The next match of the zone saw the Andhra team played against the Hyderabad team at Kothagudem from 9-11 December, 1989. The match remained drawn during the specified period of time and the match officials awarded the Hyderabad and Andhra teams 18 and 8 points, respectively for the match.

The Karnataka and Kerala teams then played against each other in the seventh of the South Zone league matches in the Ranji Trophy, 1989-90 at Hassan from 16-18 December, 1989. Playing very well in the match, the Karnataka team won the match with a good margin of an innings and 118 runs and also earned 24 points from it. The Kerala team earned 3 points from the match as well. The Kerala team appeared in the next match of the zone also and this time it played against the Goa team at Margao from 23-25 December, 1989. The winner of the match was the Kerala team with a margin of 7 wickets and the team earned 19 points from the match. The Goa team also earned 8 points from the match. The next match of the zone involved teams from Andhra Pradesh and Karnataka and the match was held at Vijayawada from 24-26 December, 1989. The match was won by the Karnataka team with a very good margin of an innings and 43 runs and the team earned 23 points from the match. The Andhra team earned 4 points from the match.

The teams of Kerala and Hyderabad played against each other in the tenth of the South Zone league matches in the Ranji Trophy, 1989-90 at Thiruvalla from 13-15 January, 1990. Hyderabad and Kerala teams earned 15 and 9 points respectively from the drawn match. The Karnataka team then played against the Goa team in the next match of the South zone and the two teams played the match at Sirsi from 13-15 January, 1990. The Karnataka team played very well in the match and clinched a huge victory of 10 wickets while earning 18 points. On the other hand the Goa team also earned 6 points from the match. The next match of the zone was held between the teams of Andhra and Tamil Nadu was also played during the same timing from 13-15 January, 1990 at Srikakulam. The winner of the match was the Tamil Nadu team with a very good margin of an innings and 78 runs and the team earned 22 points also. The Andhra team also earned 4 points from the match.

The Tamil Nadu team appeared in the next match of the zone also and it played against the Hyderabad team at Tiruchi from 20-22 January, 1990. The Hyderabad team earned 14 points and Tamil Nadu earned 10 points from the drawn match. The next match of the zone saw the Kerala and Andhra teams playing against each other at Malapuram from 20-22 January, 1990. The match remained drawn during the stipulated duration and the match officials awarded the Kerala and Andhra teams 14 and 10 points respectively. The last of the South Zone league matches in the Ranji Trophy, 1989-90 involved the teams like Tamil Nadu and Goa and the two teams played the match at Madras from 27-29 January, 1990. The Tamil Nadu team earned 24 points from the match by clinching a victory of an innings and 73 runs and the Goa team also earned 4 points from the match.