To prepare teachers for blended teaching, this study proposed ongoing teacher professional development activities that utilize the learning-by-doing approach within a professional learning community with the objective of developing the technological, pedagogical, content knowledge (TPACK) of teachers. The study explored the TPACK of 11 teachers and their perceptions of blended teaching through interviews and questionnaires. Analyses of interview data demonstrated that teachers perceived the technological benefits (e.g., supporting citywide resources) but noted that the teacher professional development training required high levels of self-regulation skills. The questionnaire results indicated significant improvements in TPACK, TCK, and TPCK but not for other dimensions of TPACK. Lastly, the study presented discussions and implications accordingly. Copyright © 2023 Education Research Institute, Seoul National University.