The 1991 Monte Carlo Open was a men's tennis tournament played on outdoor clay courts. It was the 85th edition of the Monte Carlo Open, and was part of the ATP Super 9 of the 1991 ATP Tour. It took place at the Monte Carlo Country Club in Roquebrune-Cap-Martin, France, near Monte Carlo, Monaco, from 22 April through 28 April 1991.

The men's singles field was headlined by Stefan Edberg and Boris Becker. Other top seeds in the field were Guy Forget, Andre Agassi, and Goran Ivanišević. Ninth-seeded Sergi Bruguera won the singles title.

Sergi Bruguera defeated Boris Becker, 5–7, 6–4, 7–6^(8–6), 7–6^(7–4)