The 1991 Copa Libertadores was won by Colo-Colo of Chile after defeating Olimpia of Paraguay with a 3–0 aggregate score in the finals. The championship would mark a first for a Chilean club team in an international tournament. Twenty-one clubs from all South American countries within Confederación Sudamericana de Fútbol (CONMEBOL) participated.

Qualified teams

Draw

The champions and runners-up of each football association were drawn into the same group along with another football association's participating teams. Three clubs from Paraguay competed as Olimpia was champion of the 1990 Copa Libertadores. They entered the tournament in the Second round.

Group stage

Group 1

Group 2

Group 3

Group 4

Group 5

Round of 16

Quarterfinals

Semifinals

Finals

First leg match played on May 29, 1991, in Asunción, Paraguay at Defensores del Chaco stadium. Second leg final match played on June 5, 1991, in Santiago, Chile at Estadio Monumental David Arellano. Colo-Colo won 3-0 on aggregate.

Champion