The 1991 Portuguese Grand Prix was a Formula One motor race held at the Autódromo do Estoril on 22 September 1991. It was the thirteenth race of the 1991 Formula One World Championship.

The race was won by Italian driver Riccardo Patrese, driving a Williams-Renault, after he started from pole position. Patrese's teammate and Drivers' Championship challenger, Briton Nigel Mansell, led until a pit stop went wrong, resulting in his disqualification from the race. Brazilian Ayrton Senna finished second in a McLaren-Honda, thus increasing his lead over Mansell in the championship to 24 points with three races remaining, with Frenchman Jean Alesi finishing third in a Ferrari.