Ray J is making a major investment in his new legal marijuana biz ... and he's kicking off his very own weed venture by hawking joints named after -- who else -- himself!!!

Our Ray J sources tell TMZ ... he's already poured in $5,000,000 to fire up a cannabis company in Cali, and the first rollout will feature pre-rolled joints, dubbed, "Ray Jay's."

As you see in the video, Ray J ain't playing around when it comes to his plants ... he's already got a greenhouse stocked with rows and rows of dank, and the flowers look like the stickiest of the icky!!!

The company is called William Ray LA, and Ray J's assembling a top-notch gang of ganja experts specializing in growing, branding and marketing herb ... and he's going to put his stamp on the biz with his own personal knowledge and expertise. See, smoking pot has tons of benefits!!!!

Ray's manager, David Weintraub, tells us the company's aim will focus on non-traditional marketing strategies in media, music and entertainment.

Sativas and indicas aren't the only things Ray J is hawking ... his enterprise will also offer services to other growing companies looking to expand their reach. Ray J has big plans to expand throughout the country.

Ray J and Mary J ... now that's a vibe.