Guns N' Roses' bass player, Duff McKagan, is the proud owner of an adorable new pup ... a rescue he picked up with his boo as a brand new addition to their family.

Duff and his wife, Susan Holmes McKagan, rescued the little one Monday from The Labelle Foundation in Los Angeles -- an organization that's all about rescuing, rehabbing, and advocating for dogs.

The doggo is a chihuahua-terrier mix and is just about as adorable as it sounds.

And if ya still aren't on board, check out this clip of it running around in the grass ... awww!!!

BTW, Guns N' Roses just wrapped the North American leg of its latest tour -- closing out with a couple of shows at The Hollywood Bowl and a killer concert at Hell And Heaven Fest in Mexico.

Translation ... Duff and Susan have some time on their hands to train their adorable dog.