Mindfulness and Acceptance-Based Group Therapy (MAGT) for Social Anxiety Disorder (SAD) is based largely on Acceptance and Commitment Therapy (ACT; Hayes et al., 1999), with enhanced mindfulness mostly from Mindfulness-Based Cognitive Therapy (MBCT; Segal et al., 2002). The purpose of this study was to assess the feasibility and initial effectiveness of MAGT for the treatment of SAD. Forty-two SAD patients were invited to take part in an open trial of MAGT. Participants completed measures of social anxiety, mindfulness and acceptance, depression, and rumination at pretreatment, midtreatment (6 weeks), posttreatment (12 weeks), and at a 3-month follow-up session. Twenty-nine participants completed the treatment and these participants reported that the treatment was helpful. Effect sizes for treatment completers ranged from 1.00 to 1.17 for the social anxiety symptom measures at follow-up. Intent-to-treat analyses revealed significant reductions in social anxiety, depression, and rumination and significant increases in mindfulness and acceptance, with effect sizes ranging from .65 to .76 on the social anxiety measures. This study demonstrates that MAGT is feasible and acceptable to SAD patients and provides further support for the use of mindfulness and acceptance-based interventions for the treatment of SAD. (Contains 1 figure and 3 tables.)