To elucidate the effects of medium-chain fatty acids (MCFA) on milk production and plasma metabolite and hormone concentrations in early lactating dairy cows, 10 multiparous Holstein dairy cows were randomly assigned to two dietary treatment groups after parturition. One group was fed a diet supplemented with calcium salts of MCFA (MCFA-Ca) for 8 weeks after parturition, while the other group was fed the same diet without the supplement (control). MCFA-Ca, containing 60% caprylic acid and 40% capric acid, was added to a total mixed ration (TMR) at 1.5% of the dietary dry matter (DM). Cows were offered the TMR ad libitum. DM intake, daily gain in bodyweight, milk yield, milk fat content and milk protein content did not differ between the two treatment groups. The MCFA-Ca diet decreased plasma glucose and triglyceride concentrations (P < 0.05), while plasma concentrations of total and free cholesterols tended to increase (P < 0.10). Plasma ghrelin was maintained at a higher concentration (P < 0.05) in cows fed the MCFA-Ca diet than in the control group. Relative to the control diet, the MCFA-Ca diet decreased plasma insulin concentration (P < 0.05) and numerically increased plasma glucagon concentration, resulting in a lower insulin : glucagon ratio (P < 0.05). In conclusion, plasma metabolite and hormone concentrations were affected by the MCFA-Ca diet, suggesting that MCFA-Ca supplementation may change endocrine functions and nutrient metabolism in early lactating cows, ultimately resulting in an enhanced catabolic state.