This study evaluated the overall effectiveness and tolerability of adjunctive quetiapine as a continuation therapy for the long-term treatment of bipolar mania. Twenty-three patients were enrolled in this study and received quetiapine add-on treatment in combination with their existing or new mood stabilizers. The clinical assessment was carried out using the Young Mania Rating Scale (YMRS), Clinical Global Impression-severity(CGI-s), Hamilton Depression Rating Scale scores-17 item, Simpson-Angus Rating Scale and Barnes Akathisia Rating Scale at the baseline, 1, 4, 12 and 24 weeks. The YMRS and CGI-s decreased significantly from the baseline to the endpoint by 89.7% and 78.3%, respectively (p < 0.0001; p < 0.0001). By the end of the study, 22 patients showed at least 50% improvement in the YMRS score. This study suggests that quetiapine can be used as an adjunct in the long-term treatment of bipolar mania.