The objective of this study was to investigate the infection rate of gastro-intestinal tract parasites on acquired laboratory nonhuman primates, Vervet monkey, Cynomolgus monkey, and Rhesus monkey acquired from Japan and China. These monkeys have been acclimating at an individual housing condition after our legal quarantine period. We examined 133 fecal samples to investigate parasitic infection using direct smear and formalin-ether-sedimentation technique. As a result, total parasitic infection rate was 33.8% (n=45/133) for all monkeys. Two species of macaques, cynomolgus and rhesus, were infected with Trichuris trichiura (4), Giardia lamblia (4) and Balantidium coli (41). Vervet monkeys, which had been controlled by individual housing system for a long time, were clear for parasitic infection. The protozoan, Balantidium coli was one of the most frequently detected in these monkey colonies. Double infection was noted in only 4 monkeys and involved with Trichuris trichiura and Balantidium coli. Serious clinical symptoms were not observed in the most of the infected monkeys, but the monkeys infected by Giardia lamblia showed intermittent or chronic watery diarrhea. Consequently, the prophylactic anthelmintic treatment and periodic monitoring are essential to preserve the SPF colonies in the laboratory facility.