Objective To examine the relation between compensatory sweating（CS） and the resection site of the sympathetic nerve china during sympathectomy in treatment of palmal hyperhidrosis and thus to investigate the potential mechanism of the occurrence of compensatory sweating. Methods From October 2004 to December 2005, 128 patients with primary palmar hyperhidrosis were randomly divided into two groups： 61 with T3 sympathicectomy （T3 group） and 67 with T4 sympathicectomy （T4 group）. All were treated under general anesthesia, single lumen intubation and via intercostal mediastinoscopic surgery. Results No morbidity or mortality occurred. Sweating of target organs was cured in all cases. Rates of minor CS in Group T3 or T4 showed no statistically significant （χ^2 = 1.866, P = 0.122）. Rate of moderate CS in group T4 was significantly lower than that in group T3 （χ^2=7.618, P=0.006）. No severe CS occurred. Conclusion Occurrence rate and severity of compensatory sweating are lower in T4 resection than in T3.