The season was divided into two stages. In the first stage, each team played the others twice (a double round robin system) for a total of 18 games. Teams received two points for a win and one point for a draw. No points were awarded for a loss. The teams carried their records from the first stage into the second stage. In the second stage, the teams were separated into two groups; an upper-table group and lower-table group. Each group played a further 4 games against the teams in their group. The upper group played for the league title and the lower group played to avoid relegation. The season champion and runner-up qualified for the
1966 Copa Libertadores. Two points were awarded for a win, one point for a draw, and no points for a loss. == Teams ==