All the four teams that have been playing in the previous editions of the Ranji Trophy under the East Zone did play in the same zone in the Ranji Trophy, 1965-66. The teams were the likes of Assam, Bengal, Bihar and Orissa and coming from the Eastern region of India, all of them played against each other for entering into the knock out level. The toppers of the East Zone in the Ranji Trophy, 1965-66 were the teams like Bengal and Bihar and they competed with the top teams of the other zones in the knock out level of the tournament.

The East Zone league matches in the Ranji Trophy, 1965-66, started with the match between the teams of Assam and Orissa and the match was held at Cuttack from 12-14 December, 1965. The match was drawn during the stipulated duration and the Assam and Orissa team earned 5 and 3 points, respectively from the match. The second match, involving the teams of Bihar and Assam, was held at Jamshedpur from 18-20 December 1965. The Bihar team got a good start in the tournament, as it won the match by 7 wickets to earn 8 valuable points from it.

The teams of Orissa and Bengal then clashed with each other in the third of the East Zone league matches in the Ranji Trophy, 1965-66. The match was held at Cuttack from 18-20 December, 1965 and it saw the Bengal team winning by a huge margin of an innings and 3 runs and earning 3 points from the match. The Bengal team then played against the Assam team in the next match that was held at Calcutta from 24-26 December, 1965. The Bengal team played wonderfully in this match also and clinched a huge victory of an innings and 168 runs to earn 8 valuable points from the match.

There was a clash between the teams of Bihar and Orissa in the fifth of the East Zone league matches in the Ranji Trophy, 1965-66 and the match was held at Cuttack from 25-27 December, 1965. The Orissa team played astonishingly well in this match and surprised the Bihar team by defeating them with a margin of 51 runs. The Orissa team earned 8 valuable points from the match, as well. The last match of the East Zone saw a battle between the heavyweight teams of Bengal and Bihar at Jamshedpur from 01-03 January, 1966. The drawn match saw both the Bengal and Bihar teams earning 3 points each from the match.