Twenty‐six young participants, 18–25 years, with social phobia (SP) were randomly assigned to eight 2‐hour sessions of group mindfulness‐based cognitive therapy (MBCT) and twelve 2‐hour sessions of group cognitive‐behavioral therapy (CBT) in a crossover design with participants receiving treatments in reversed order. Outcome was assessed after treatments, and at 6‐ and 12‐month follow‐ups. MBCT achieved moderate‐high pre‐post effect sizes (d = 0.78 on a composite SP measure), not significantly different from, although numerical lower than those of CBT (d = 1.15). Participants in both groups further improved in the periods following their first and second treatment until 6‐months follow‐up (pre‐follow‐up ds = 1.42 and 1.62). Thus, MBCT might be a useful, low cost treatment for SP, although, probably, less efficacious than CBT.