A perv tried to rape a woman in the laundry room of her Brooklyn apartment building, cops said on Saturday.

The 30-year-old victim was washing her clothes in the building at Lincoln Road and Flatbush Avenue in Prospect Heights around 7:30 a.m. Friday when a stranger barged in, approached her with his pants down and exposed himself, cops said.

Then he demanded the woman have sex with him — and she refused, police said.

“Don’t scream, I have a knife,” he told the woman before sexually assaulting and trying to rape her, police said.

The terrified woman managed to break free, and ran to tell a neighbor, who called 911.

The suspect ran off.

The attacker, depicted in a police sketch released Saturday, is in his mid-20s and around 6-foot-4 with a muscular build. He was last seen wearing a black hat, black sweatshirt and black sweatpants, cops said.