Officers were called to 140 West 87th Street at 8 a.m., where they discovered the 5-foot long reptile inside the kitchen sink of the apartment.
The snake was removed from an outdoor fence and turned over to the ASPCA.
Someone in the building told police they observed the snake going in the basement apartment.
It's unclear who owns the snake or where it came from.
Boa constrictors are illegal to own in New York City, according to Animal Care Centers of NYC.
The snake has been placed with a foster guardian outside of New York City.
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