Marbling characterized by the amount and distribution of intramuscular fat (IMF) in longissimus muscle (LM) and measured as beef marbling score (BMS), is an economically important trait of beef cattle in Japan. The myosin binding protein C, slow type (MYBPC1) gene, involved in efficient energy metabolism and homeostasis during muscle contraction in slow skeletal muscle, has been previously shown to be expressed at different levels in the LM between high-marbled and low-marbled steer groups using differential-display PCR (ddPCR). In this study, we found that IMF area (%) in the sacrococcygeus muscle (SM) was positively correlated with BMS in the LM in Japanese Black steers (n=22, r=0.941, P<0.0001). This suggested that the IMF area (%) in the SM tends to equate marbling level in the LM. Furthermore, we showed that the MYBPC1 expression level in SM was significantly higher in the Japanese Black steers (n=5) with high BMS than in the Japanese Black steers (n=5) with low BMS (P<0.001). Moreover, correlation analyses showed that the expression level of the MYBPC1 gene was positively correlated with IMF area (%) (n=22, r=0.858, P<0.0001) and BMS (n=22, r=0.769, P<0.0001), indicating the association of MYBPC1 expression level with marbling trait. These results, together with the previous ddPCR result, suggested that high level of MYBPC1 expression may be associated with the development of marbling in Japanese Black beef cattle.