Jake Paul is celebrating the launch of his new W body care line in the flashiest way possible ... by getting a $650k diamond pendant and chain to rep the brand!!

TMZ Sports has learned Paul -- a 9-1 cruiserweight boxer, Internet sensation and businessman -- hit up his go-to jeweler Vobara in Miami to make him a piece in honor of his newest endeavor.

Vobara -- who has made pieces for celebs like Rick Ross, Udonis Haslem and DJ Khaled -- made sure the pendant looked just like the W logo ... and we're told it's filled with VS/VVS diamonds including 20, 50 and 80 pointers in a mosaic setting.

There's even a small version of the W body spray bottle on the back of the pendant.

The pendant and massive Cuban link chain were made with 1,500 grams of 14k white gold and an insane 300 carats in diamonds -- a total value of a whopping $650,000!

We're told it took Vobara two months to put together... and he said he's honored El Gallo reached out to him to bring the whole thing together.

"It's only right he made that major statement getting fully iced-out in gold," Vobara told us. "Proud of him, he's going to turn that company into something major. He's a smart kid."

Paul is scheduled to fight Mike Perry on July 20 ... so don't be surprised if you see the W chain on his neck when he walks to the boxing ring!!