91 Aegina (e-jye'-na) is a large main belt asteroid. Its surface coloring is very dark and the asteroid has probably a primitive carbonaceous composition.

It was discovered by a French astronomer Édouard Jean-Marie Stephan on November 4, 1866. It was his second and final asteroid discovery. The first was 89 Julia. The asteroid's name comes from Aegina, a Greek mythological figure associated with the island of the same name.