This paper aims to investigate the high school Biology teachers’ opinions toward lesson study (LS). A cross sectional survey integrating both quantitative and qualitative methods was conducted among 91 high school Biology teachers (HSBTs) in CanTho City. The results revealed that a high percentage (76. 9%) of HSBTs got LS training; however, many of them have misconception about the LS definition. Another result found was that some HSBTs were satisfied and some were unsatisfied with LS training, and they want intensive LS training, more practice with themselves, and get real experiences and real activities in the training program. The most important clinically relevant finding was, most HSBTs misunderstand the process of LS and the principle of LS, especially observation and reflection. Thus, they have difficulties in applying LS in their teaching. The main reasons for this opinion include: stressfulness, fear of other people recognizing their shortcoming about knowledge and method, weakness in assessment, and different standpoints in observation time. Observing teachers criticize and make observed teachers feel recessive, unhappy or upset in the reflection time. In addition, many Biology teachers do not realize the value of observation and feedback from other teachers. Therefore, further intervention research should be done to investigate the applying of LS cycle training, and the training that further focuses on right participants, who will directly implement LS, and is carefully organized to capture key points and to use abundant active training approaches.