The plasma pharmacokinetics and mammary excretion of eprinomectin were determined in dairy yaks following topical administration at a dose of 0.5 mg/kg. The kinetics of plasma and milk concentrations were analyzed using a noncompartmental model. Plasma and milk concentrations of eprinomectin increased to reach maximal concentrations of 5.45 ± 2.84 and 2.29 ± 0.90 ng/mL at a Tmax of 1.79 ± 0.57 and 2.00 ± 0.82 days, respectively. The concentration of eprinomectin in plasma was remained >0.5 ng/mL for more than 30 days after administration. The mean residence times of eprinomectin in plasma and milk were 14.73 ± 6.22 and 9.37 ± 2.81 days, respectively. The AUC value in plasma (55.89 ± 18.16 ng day/mL) was threefold greater than that in milk (18.02 ± 6.48 ng day/mL). The AUC milk/plasma ratio was 0.33 ± 0.08. The systemic availability of eprinomectin in yaks was lower than that observed value in other domestic bovines. The low level of eprinomectin excretion in milk suggests that eprinomectin can be used in yaks with zero milk-withdrawal time. The efficacy of eprinomectin against naturally acquired larvae of Hypoderma spp. was also determined in yaks. Topically administrated eprinomectin at a dose of 0.5 mg/kg was 100% efficacious against larvae of Hypoderma bovis, H. lineatum, and H. sinense.