Rob Lowe -- Doggy-Style Rescue Mission

Rob Lowe is saving lives -- doggy lives.

Sources close to the actor tell TMZ -- Rob, his brother Chad, and his son Matthew have been volunteering with OneDogRescue.org for the past six months ... coordinating adoption events, renting mobile spay/neuter clinics, and even buying toys for the pooches.

We're told Rob's son is especially involved in the rescue process -- regularly visiting the pups, and even checking up on them in foster homes to make sure they're doing ok.

ODR works primarily with special needs dogs -- like "Kenny G" -- who broke his front legs when his abusive owner threw him out a window.