This study monitored 11 subjects attending critical thinking instruction in-service training for 70 hours (one semester). The post-in-service training evaluation, interview, and c1ass observation were used to understand the real condition of critical thinking instruction at the secondary school level. The collective data were analyzed by qualitative methods.The major findings of this study are as following: 1.The effectiveness of long-term (one semester) in-service training was significant. Each subject recognized the importance of critical thinking instruction and continuously implemented the teaching method in classes after in-service training.2.The effective teaching strategies were induced by subjects' critical thinking instruction.