This investigation adjusted the lesson study (LS) model for the initial teacher education aiming to examine its effect in the development of the pre-service teachers' pedagogical content knowledge (PCK) namely, both their knowledge and understanding on how to transform a science topic to make it more understandable for the students. The LS topic was the speed of sound that is taught in the 8th grade. The PCK construct was evaluated, as well as and in terms of both PCK-topic specific knowledge and PCK-pedagogical knowledge. The participants on this investigation were three pre-service teachers. The data were collected through video recording of LS sessions. The qualitative data collection was combined with quantitative and qualitative analysis procedures. The results showed that the LS promoted an improvement on pre-service teachers' PCK as well as in most of the aspects of both PCK-topic specific knowledge and PCK-pedagogical knowledge. PCK's aspect' 'Strategies for pupil self-evaluation' has not improved satisfactorily. These findings suggest that LS should be carried out during the training programs of the science PSTs.