Background: Bcl-2 and Bcl-XL has been known to be members of Bcl-2 family for regulation of long-term cell survival. We investigated the expression of Bcl-2 and Bcl-XL in myblast during myogenesis. Methods: Cultured myoblasts from the C2C12 mouse cell line were isolated at the different stages of myoblast and myotubes. The mRNA levels for Bcl-2 and Bcl-XL were determined by reverse-transcriptase PCR (RT-PCR). The immunocytochemical staining using the antibodies for Bcl-2 and Bcl-XL was performed to examine the expression of Bcl-2 and Bcl-XL in cultured C2C12 cells. Results: By immunocytochemistry, Bcl-2 was strong expressed in cultured myoblasts compared with myotubes. The expression of Bcl-XL were observed at similar degree in both myoblasts and myotubes. The RT-PCR assay showed that C2C12 cells expressed both Bcl-2 and Bcl-XL mRNA level with different pattern of expression at differential stage. The level of expression of Bcl-2 mRNA was observed most highly at early stage of myoblasts, but diminished as differentiation progressed. However, the level of expression of Bcl-XL didn’t changed during myoblast differentiation. C o n c l u s i o n s: Bcl-2 was mainly expressed myoblastic differentiation at the early stage, whereas Bcl-XL w a s expressed during whole stages of myoblastic differentiation. These findings suggest Bcl-2 is one of marker of myoblast differentiation and may play a role in normal differentiation of skeletal muscle.