Kim Kardashian has arrived in New Orleans for the Serena Williams wedding extravaganza -- and she's already got one outfit change under her belt.

Kim slipped into a tight black dress after her plane landed Thursday afternoon -- we're guessing she was heading straight from the airport to the ceremony.

We're told Kanye didn't make the trip. Unclear why.

The wedding is set to begin in the next few hours -- and we're told there will be a bunch of HUGE stars in attendance when Serena trades I Dos with Alexis Ohanian.