Objective To evaluate the effectiveness and safety of AAI pacing mode versus DDD pacing mode for treating sick sinus syndrome (SSS). Methods We electronically searched CENTRAL (Issue 2, 2009), MEDLINE (1980 to June 2009), EMbase (1980 to June 2009) and CBM (1990 to June 2009). Randomized controlled trials (RCTs), quasi- RCTs and cross-over studies were identified and assessed, and then RevMan 5.0 software was used to perform metaanalysis. Results A total of 509 patients of six parallel and two crossover RCTs were identified, and the quality of reporting was found poor. Studies showed a statistically significant preference to AAI pacing mode for the reduction of left atrial diameter (MD=2.09, 95%CI 0.22 to 3.97), left ventricular end-diastolic diameter (MD=3.00, 95%CI –1.58 to 7.58), the prevention atrial fibrillation (P=0.026) and the improvement of life quality (Plt;0.05), but with more replacement or remodulation. Non-significant preference was shown to the prevention of all-cause mortality (P=0.51), cardiovascular mortality (P=0.43), stroke (P=0.32) and heart failure (P=0.17), the reduction of left ventricular end-systolic diameter (MD=1.21, 95%CI –0.85 to 3.28) and left ventricular ejection fraction (MD= –2.91, 95%CI –6.53 to 0.70). No significant adverse effects were reported. Conclusion The review shows a trend towards AAI pacing mode compared with DDD pacing mode in terms of effectiveness. However, because of the high bias risk of the included trials, the evidence is insufficient, so more large-sample and high-quality RCTs are needed.