Kim Kardashian, Katy Perry Dress Hot for Lauren Sanchez's Bachelorette Party

Kim Kardashian and Katy Perry aren't just having a Parisian girls' trip ... they're in town to celebrate Lauren Sanchez's impending nuptials -- and, they're looking great while doing it.

The two stars stepped out in the City of Lights Friday to celebrate Sanchez ... with Kim pulling up in a strapless black dress that accentuated her cleavage.

While the dress had a train in the back, it did little to hide her legs in the front ... though her stockings added an extra layer of mystery to the outfit.

Perry wore a tiny top, skintight mesh leggings ... channeling another big pop star in Madonna while she stopped to sign some autographs for fans.

Kris Jenner and Eva Longoria also made it to the event ... Kris in classic black and Eva's wearing a vibrant blue dress.

While everyone else seemed to wear black or other dark colors, Sanchez left no doubt about who was getting married -- throwing on a skimpy white dress and flashing a huge grin while she and her pals headed to a party boat on the Seine.

This isn't the first day of festivities ... 'cause Lauren was out with Kim and Katy Thursday too -- leaving a dinner joint together.

Lauren's expected in Cannes soon enough for the annual film festival in the city -- though her look-alike already made an appearance -- where she'll accept an award for her philanthropic work.