This research investigated the development of critical thinking of middle school chemistry teachers in Shaanxi province of China. In-service and pre-service teachers' critical thinking are examined in order to provide evidence for establishing teachers' standard. The sample in this study consisted of 69 in-service and 61 pre-service chemistry teachers. The California Critical Thinking Disposition Inventory (CCTDI) and California Critical Thinking Skills Test (CCTST) are used to assess the teachers' critical thinking. The results indicate that the teachers' dispositions toward critical thinking are at an average level while their scores of critical thinking skills are very low. This research also shows there are statistically significant differences between in-service and pre-service teachers in their critical thinking skills, but no significant difference in their critical thinking dispositions. Additionally, both CCTST and CCTDI mean scores reflect that the pre-service chemistry teachers performed better than the in-service teachers toward critical thinking. (Contains 3 tables and 2 figures.)