Purpose: This study was a systematic review and meta-analysis of the effects of exercise programs in patients with type II diabetes mellitus. Method: Two investigators systematically searched and reviewed English articles from PUBMED from 1988 to 2004, selecting randomized controlled trials on structured exercise programs for DM patients. Out of 87 studies identified, a meta analysis was done for eleven studies which satisfied inclusion criteria and focused on glycemic indices, lipid indices, and cardiac function indices. Results: The means and standard deviations were compared for experimental groups that received exercise-only or exercise and diet programs and control groups that received no intervention or only diet education. The groups were considered homogeneous as the p value of the Q score in each variable group was over 0.05. The experimental groups demonstrated a moderate positive effect on HbA,c and $VO_{2max}$ (d=0.55 & 0.5), and a small positive effect on fasting blood glucose and cholesterol (d=0.38 & 0.27) compared to the control groups. HDL and LDL cholesterol levels, however, showed a very low positive effect (d=0.11 & 0.12) in the experimental groups. Aerobic exercise was more beneficial than resistance exercise on $HbA_1c$ (d=0.59 vs 0.28) in the groups. Conclusions: Regular exercise has a positive effect on $HbA_1c$, fasting blood glucose, total cholesterol, HDL cholesterol, LDL cholesterol, and $VO_{2max}$ in Type 2 diabetic patients.