This experiment was conducted to evaluate the effet of fat supplementation on feed intake, rumen fermentation and milk production in cows. 8 Holstein (2 primiparous and 6 multiparous) were used in a replicated 4x4 Latin quare design with 28-d periods. All cows were fed forage ad libitum and were assigned to one of four Isonitrogenous diet groups: (1) control, (2) 4.5% tallow, (3) 4.5% whole cotton seed, and (4) 4.5% Calcium soap. Fat supplementation did not affect milk yield and composition, but tended to decrease the dry matter intake. Rumen pH reached the lowest point at 3 hrs after concentrate feeding, but was not affected by supplemental fat feeding. The VFA was highest in calcium soap group at 2 to 4 hours post feeding than the other groups. Fat supplementation had no effect on lactational performance although they have decreased in dry matter intake. The body weight also has no difference among the treatment group.