Odell Beckham Rocks $650k Diamond Chain At Met Gala

Odell Beckham had one of the most expensive outfits at the Met Gala ... and it's all thanks to his incredible $650k diamond chain!!

TMZ Sports spoke with OBJ's go-to guy, Gabriel the Jeweler ... who tells us the wide receiver copped the ice right before Monday's big event.

Beckham donned a green velvet hoodie for the Gala ... accenting it with the massive chain and rings.

The chain is truly one of a kind -- we're told it's made with 300 carats of round diamonds, 200 carats of emerald-cut diamonds and 2 1/2 kilos of gold.

Of course, Gabe is the mastermind behind some of OBJ's most iconic pieces ... and has worked with superstars like Antonio Brown, Fernando Tatis, Joe Mixon and more over the years.

Other athletes at the Gala include Russell Westbrook, Dwyane Wade, Chloe Kim and Venus Williams ... who all killed it with the "Gilded Glamour" theme.