Non-human primates have been increasing in demand as important experimental animals and companion animals, domestically and internationally. The number of non-human primates for these purposes will be much enhanced in the near future. Despite this trend, basic physiological data are scarcely available in these animal species, leading to the difficulty to diagnose diseases when necessary, due to the absence of reference values. Particularly, there is not any report on the total activity of LDH of non-human primates, let alone LDH isoenzyme patterns, in Korea. LDH isoenzymes have a high level of efficaciousness as diagnostic and prognostic aids in various diseases. In this study, total activities and isoenzyme patterns of LDH were measured to obtain their reference values in domestically reared common marmosets, crab-eating macaques and Japanese macaques. There were widespread different values of serum total LDH among the non-human primate species experimented in this study. Serum LDH values of common marmosets and crab-eating macaques were 597.5$pm$243.1 IU/l and 605.3$pm$312.6 IU/l, respectively, whereas those of Japanese macaque showed 1,209$pm$473.8 IU/l. Five isoenzyme fractions of LDH were observed in all experimented non-human primates but their ranks and proportions represented different patterns one another. In common marmosets, the percent of fraction for serum LDH1, LDH$_2$, LDH$_3$, LDH$_4$, and LDH$_{5}$ was 13.7$pm$6.4%, 23.3$pm$3.6%, 29.2$pm$5.0%, 9.4$pm$1.4% and 24.4$pm$7.5%, respectively. The rank of LDH isoenzymes was LDH$_3$>LDH$_{5}$>LDH$_2$>LDH$_1$>LDH$_4$, in the descending order. For crab-eating macaques, the fraction of serum LDH$_1$, LDH$_2$, LDH$_3$, LDH$_4$, and LDH$_{5}$ occupied 19.5$pm$12.7%, 25.3$pm$9.3%, 23.8$pm$8.1%, 10.2$pm$2.8% and 21.3$pm$14.2%, respectively. The order of LDH isoenzymes was LDH$_2$>LDH$_3$>LDH$_{5}$>LDH$_1$>LDH$_4$, from top to down. On the while, in Japanese macaques, the fraction of serum LDH$_1$ to LDH$_{5}$ showed 23.4$pm$11.8%, 30.5$pm$4.1%, 17.4$pm$3.9%, 11.3$pm$3.7% and 13.8$pm$5.6%, respectively. The decreasing order indicated LDH$_2$>LDH$_1$>LDH$_3$>LDH$_{5}$>LDH$_4$. In conclusion, values such as LDH and LDH isoenzyme patterns of investigated for the first time from non-human primates reaared in Korea, could be reference values for the optimal diagnosis and therapy of diseases of the corresponding animal species. Other parameters of hematology and blood biochemistry are urgently needed to study for the benefit of our intimate non-human primates.an primates.