Effects of low or high starch diets with or without supplemental fat on the yield of milk and milk components and energy partitioning were evaluated. Thirty-two Holstein cows (172 ± 35 DIM) were assigned randomly to treatment sequence in replicated 4 × 4 Latin squares with a 2 × 2 factorial arrangement of treatments. Treatment diets contained 16% (LS) or 32% (HS) starch and 0.0% (LF) or 1.5% (HF) palmitic acid-enriched fat supplement (BergaFat F-100). Dietary starch was altered by varying the proportion of ground corn, cottonseed, and soyhulls, with LS and HS diets containing 17 and 21% forage NDF and 42 and 29% NDF, respectively. Treatment periods were 21 d in length with the final 5 d used for data and sample collection. The statistical model included the random effects of cow and period and the fixed effects of dietary starch level, fat supplementation, and their interaction. Compared with LF, the HF treatment increased DMI in the LS diet (26.8 vs. 25.8. kg/d) and decreased DMI in the HS diet (25.9 vs. 26.5 kg/d; interaction P < 0.01). The HF treatment increased milk fat yield in the LS diet (1.57 vs. 1.51 kg/d) but not in the HS diet (1.49 vs. 1.51 kg/d; interaction P = 0.06). Compared with LF, the HF treatment also increased milk protein concentration and yield in the LS diet (3.40 vs. 3.35% and 1.31 vs. 1.26 kg/d), but not in the HS diet (interaction P = 0.10 and P < 0.05, respectively). There was no effect of treatments on milk fat and lactose concentrations or lactose yield. Compared with LF, the HF treatment increased 3.5% FCM (42.2 vs. 41.0 kg/d) in the LS diet but not in the HS diet (40.4 vs. 41.1 kg/d; interaction P = 0.07). Similarly, the HF treatment increased ECM (42.3 vs. 41.0 kg/d) in the LS diet but not in the HS diet (40.5 vs. 41.2 kg/d; interaction P < 0.05). The milk to feed ratio (ECM/DMI) was not affected by treatments. There was a trend for HS diets to increase change in BCS compared with LS diets (P = 0.08). However, fat supplementation did not affect change in BCS. Results demonstrate that under the dietary conditions tested, a palmitic acid-enriched fat supplement fed to mid and late lactation dairy cows maximized yield of milk and milk components when fed in a low starch diet.