Four Holstein steers (261 +/- 2 kg) with cannulas in the rumen and proximal duodenum were used in a 4 x 4 Latin square experiment to evaluate the interaction of dietary Ca (.45 vs. 90%) and supplemental fat (0 vs 5% yellow grease) on characteristics of digestion. There were no treatment interactions (P > .10). Supplemental Ca did not influence (P > .10) digestibility of OM, NDF, starch, N, and fatty acids. Supplemental fat decreased ruminal (21%, P < .05) and total tract (3%, P < .01) digestibility of OM and ruminal (25%, P < .10) and total tract (20%, P < .01) digestibility of NDF. Supplemental fat increased (P < .10) ruminal microbial efficiency. Ruminal free Ca was not affected (P > .10) by Ca intake but was closely associated with ruminal pH and fatty acid intake (R2 = .84). Apparent ruminal Ca absorption was generally negative, being increased (P < .05) by Ca supplementation and decreased (P < .10) by fat supplementation. Postruminal (P < .05) and total tract (P < .01) apparent Ca absorption was increased by Ca supplementation. Supplemental fat did not influence (P > .10) postruminal or total tract Ca absorption. One hundred forty-four medium-frame crossbred steers were used to evaluate treatment effects on feedlot growth performance. There were no treatment interactions (P > .10). Increasing dietary Ca did not influence (P > .10) steer performance. Supplemental fat decreased (P < .01) DMI and increased NE value of the diet (P < .01). It is concluded that increasing dietary Ca from .45 to .9% in high-grain finishing diets will not affect the feeding value of supplemental fat and that high levels (5%) of supplemental fat will not have a detrimental effect on Ca absorption.