The experiment objective was to determine whether feeding beef cattle vitamin D3 or two compounds biosynthesized from vitamin D3 (25-hydroxyvitamin D3 and 1.25-dihydroxyvitamin D3) can improve the tenderness of beef. Preliminary experiments were conducted to determine the optimal dose of each of the two derivatives of vitamin D and the best time to harvest the steers after feeding the derivatives. Four days after feeding 125 mg of 25-hydroxyvitamin D3 and three days after feeding 500mg of 1.25-dihydroxyvitamin D3 were the respective optimal kill times and dosages. Results indicate that vitamin D3 and 25-hydroxyvitamin D3 but not 1.25-dihydroxyvitamin D3, decrease Warner-Bratzler shear and increased the 3OkD protein (measures of tenderness) of relatively tender strip loins and rounds. Feeding supplemental vitamin D3 causes an increase in the vitamin D3 content of beef, which causes some concern. However, the feeding of the two vitamin D3 metabolites does not cause a residue concern. Therefore, this experiment suggests that antemortem feeding of 25-hydroxyvitamin D3 is an effective and easy way to increase tenderness of beef and may improve overall beef palatability. Future research is warranted to refine the dosages of each of the vitamin D3 metabolites and to determine optimum administration time prior to slaughter in order to achieve maximal tenderization effect.