The 1991 Lion Cup was the ninth edition of the Lion Cup, the premier domestic rugby union knock-out competition in South Africa.
All 25 South African provincial teams took part in this competition. The semi-finalists from the 1990 Lion Cup were put into Group A and the losing quarter finalists into Group B. The remaining teams were divided geographically. Groups C and D contained nine southern teams; the four southern teams with the highest ranking were put into Group C and the other five teams into Group D (where the two lowest-ranked teams, and had to play off in a qualifying game for the Group D spot in Round One). Similarly, Groups E and F contained eight northern teams; the four northern teams with the highest ranking were put into Group E and the other four teams into Group F:
This competition was a knock-out competition. A qualifying round was held between the two lowest-ranked teams for the Group D place in Round One. In each of the first three rounds, the lower-ranked teams would have home advantage. In Round One, the teams from Group D hosted teams from Group D, while the teams from Group F hosted teams from Group F. In Round Two, the winners of the eight Round One ties played against each other for a place in Round Three. The winners of the four Round Two matches then joined teams in Group B for Round Three, with the winning teams progressing to the quarter-finals (where they were joined by the teams from Group A), followed by Semi-finals and the Final.
The fixtures were as follows: