The purposes of this study were to explore the gender differences in performance of mathematics achievement based on the National Curriculum 2005 (the Grade 1-9 Curriculum). The population of the study consisted of all the seventh graders in Tainan City on Taiwan. The results of this study were: 1. the performance due to gender were significantly different, and the female exceeded the male. 2. both of the performances in the ”algebra” and ”number” due to gender were significantly different, and the female exceeded the male. 3. DIF was present between the groups of gender. Finally, according to the results and findings of this study, there are some suggestions for the practical use and future research.