The 1990–91 Alpha Ethniki was the 55th season of the highest football league of Greece. The season began on 16 September 1990 and ended on 2 June 1991. Panathinaikos won their second consecutive and 16th Greek title.
The point system was: Win: 2 points - Draw: 1 point.
^Olympiacos were punished with a one-year ban from all European competitions by the UEFA disciplinary committee after being charged for the eventful European Cup Winners' Cup match against Sampdoria on 24 October 1990.