Taiwan's postal service has undergone a successful transformation as a state-owned public corporation since January 1, 2003. It is interesting to investigate the performance of postal service after becoming a public corporation. In this paper, we estimate technical efficiency for 61 post offices in Taichung area by a nonparametric approach known as data envelopment analysis (DEA) method. We choose the total number of mail handled (including collection and delivery), and the total number of customers served as outputs, meanwhile, the number of labor and capital-related variables are selected as inputs. Our empirical results indicate that of the post offices studied, 7 and 15 offices are evaluated as efficient based on the assumptions of CRS and VRS, respectively. On average, the pure technical efficiency of the postal offices is 0.852, implying that the postal offices should expand their outputs by 17.4 percent, keeping inputs unchanged, so as to attain technically efficient.