I don't see why not! They say to avoid caffeine at first but decaf (obviously) doesn't have any When I did South Beach, I skipped the whole "detox" or Phase 1, because I just couldn't bring myself to stop drinking my precious coffee (among the other millions of restrictions). But after adopting the SB philosophy (few carbs, more meat and veggies) I dropped 50 pounds! (I'd still be dropping more if I didn't get pregnant right afterwards!) Good luck!