The alleged incident happened last Thursday in a restroom near the running track and parking lot K.
Police said the female victim was cleaning the men's bathroom when the suspect forced her into a stall and exposed himself. He demanded a sexual favor and then ran off.
The suspect was described as a black man in his 40s, 5 feet 10 inches to 6 feet tall, weighing about 350 pounds. He had three skull tattoos across his chest and he's missing an upper right tooth.
Campus officials are warning people to be aware of their surroundings and to report anything suspicious.
Anyone with information was asked to call Cal Poly Pomona police at (909) 869-3399.