The purpose of this study aimed to investigate the operating performance of 30 Major League Baseball (MLB) teams in 2009. Research method included Data Envelopment Analysis (DEA). We set the team's total salary paid to players as an input measurement and three output measurement including team record, ranking and the average attendance per game through the CRS model and the VRS model to calculate the overall efficiency, technical efficiency, scale efficiency, the efficiency value and related materials of those 30 teams. Results showed that 4 teams reached overall efficiency where Dodgers performed the best. In addition, 11 teams reached technical efficiency and 6 teams reached scale efficiency. Two of the most important indicators affecting team performance included winning percentage and number of audiences.