The present study was to investigate the effects of supplementation of Ca and vitamin D3 in the basal diet on muscle tenderness of yellow chickens two weeks before slaughter. A total of 1 440 yellow chickens (43 days old) were used in this experiment. They were allotted to 9 groups on the basis of body weight in a 2×3 factors design; each treatment consisted of 4 replicates with 40 chickens in each replicate. The supplemental levels of Ca and vitamin D3 were as follows, Ca: 0.0%, 0.4%, 0.8%; VD3: 0, 1 000, 2 000 IU/kg Results showed that supplementation of Ca and vitamin D3 had no significant effect on growth performance of yellow chickens (P>0.05). Supplementation of vitamin D3 had no significant effect on muscle tenderness of yellow chickens (P>0.05). Supplementation of 0.4% Ca increased the muscle tenderness (P<0.05), and vitamin D3 had an associative effect with Ca, but when the supplemental level of Ca was more than 0.4%, the associative effect of vitamin D3 decreased. Supplementation of vitamin D3 had no significant effect on the activity of CaATPase and the degradation extent of troponin (P>0.05) Supplementation of 0.4% Ca increased the calpastatin gene expression （P<0.05） and had a trend to increase the activity of CaATPase and the degradation extent of troponin. It was concluded that supplementation of 0.4% Ca increased the muscle tenderness of yellow chickens, and supplementation of vitamin D3 had no effect on the muscle tenderness, but it had a cooperative effect with Ca.