Satellite cells are adult stem cells responsible for the regenerative capacity and post-natal growth of skeletal muscle. They are capable of repairing damaged muscle fibers and repopulating their own cell pool. Although typically quiescent, they can become activated and express MyoD, a muscle specific basic helix-loop-helix (bHLH) transcription factor, which is responsible for satellite self-renewal and differentiation through E-box dependent transcriptional activity. Satellite cells lose their regenerative capacity when expanded in culture due to becoming activated. The mechanisms by which satellite cells are maintained remain to be fully elucidated. Here, we cloned a bHLH transcription factor, TCF23, and investigate its function in myogenesis. Ectopic expression of TCF23 prevented the differentiation of myoblasts into differentiated myotubes by inhibiting the function of MyoD. Since the suppression of MyoD activity is an important aspect in the self-renewal of satellite cells, TCF23 suppression of MyoD would be beneficial to expanding satellite cells in culture.