The effects of calcium propionate supplementation on performance, meat quality, and mRNA expression of Wagyu steers were investigated. Eighteen steers (635 ± 20 kg; 18 ± 1 month old) were randomly divided into two groups: control (CG, without calcium propionate) and experimental (CaP, 200 g calcium propionate per steer per day). All steers were reared for 51 days under the same production system and then slaughtered at a final body weight of 680 ± 18 kg. The results showed no significant differences in dry matter intake, daily gain, or feed conversion ratio between the CaP and CG groups (P > 0.05). The treatments did not significantly affect the pH, drip loss, cooking loss, Warner–Bratzler shear, protein, fat and ash contents in meat (P > 0.05). The erucic acid (C22:1) content in group CaP was significantly lower than in CG (P < 0.05). The content of polyunsaturated fatty acids (PUFA) in CaP showed a decreasing trend compared with CG (P = 0.06). The expression of genes for peroxisome proliferator–activated receptor γ (PPARG) and CCAAT/ enhancer binding protein α (CEBPA), which are involved in adipogenesis, was significantly higher in group CaP than in CG (P < 0.05). The results indicate that supplementing calcium propionate did not affect animal performance, but changed the composition of meat fatty acids, especially PUFA and erucic acid, and could trigger upregulation of PPARG and CEBPA mRNA expression levels, which could cause long-term activation of adipogenesis. Therefore, the results of the present study point to the possibilities of improving meat quality through calcium propionate supplementation of the diet.