The 35-year-old's sexy frock could have been mistaken for a night gown as she joined husband Kanye West for an early birthday celebration at Cipriani restaurant in New York City.
Kim teamed her plunging monochrome dress with black strappy heels, and carried a black coat rather than do her usual wearing it thrown across her shoulders.
Kanye celebrates his 39th birthday on 8 June.
The superstar couple have brought their children North, two, and Saint, six months, to New York City with them. They were pictured taking North to a production of The Lion King on Broadway on Sunday, 5 June.
Kim and Kanye were in New York ahead of the Governor's Ball over the weekend, where Kanye had been scheduled to perform on the Sunday night. But bad weather meant the Randall's Island show was cancelled.
Kanye then announced he'd be holding a secret gig in the city, but it too was cancelled after more than 4,000 fans arrived at the 1,500-capacity venue.