A Queens octogenarian is the latest elderly city resident to be victimized by a heartless criminal who threatened her with a knife and stole a pricey ring.

The 85-year-old woman was robbed at knifepoint inside her own home after she advertised furniture for sale, police said.

A man responding to the furniture ad came to the victim’s Flushing apartment Wednesday morning, and ransacked the place once he got inside, authorities said.

The thief grabbed a $500 supply of alcohol and $20 worth of tea and stuffed it in a bag, cops said.

Then he demanded the woman’s ring, cops said. When she refused, the thief flashed a knife and asked a second time — when the woman complied, according to police.

The ring, valued at $4,000, was some kind of “ceremonial ring,” police said.

The suspect, captured on surveillance video, is about 45 years old, balding, around 5-foot-9 and 150 pounds, cops said.