A man snatched a 3-year-old boy sitting in his stroller outside a Brooklyn grocery store — but his grandmother chased down the kidnapper and scared him off, cops said.

The woman and her grandson were outside Thanksgiving Supermarket on 86th Street in Gravesend about 3:50 p.m. Monday when the stranger snatched the stroller under her nose and casually strolled away, police video shows.

The footage, released early Wednesday, shows the cap-wearing suspect walking behind the pink stroller as he pushes it with his right hand, keeping his head down.

He abandoned the stroller and rushed off when the grandmother chased after them, police said. The child was not injured.

Police are still looking for the attempted abductor.