Diarrhea is a common intestinal symptom in macaque. The corresponding intestinal lesions of macaque are mainly described at autopsy but less observed by colonoscopy. The aim of this study was to develop a colonoscopic technique and to obtain endoscopic images of the entire colon in macaques. Eight healthy adult macaques (5 males and 3 females) without diarrhea for 2 months, were fed Glauber's salt through nasogastric tubes. The colon cleanliness was well matched to the endoscopic observation of macaque colon. The procedure took 10-20 min for each animal. There was no obvious abnormality in the colon of four animals except some slight differences of mucosal structure from that of human beings. Small pieces of erosion and ulcer in the colons were observed in four macaques which presented mild diarrhea for less than 1 day, while a severe stenosis was observed in one of those four macaques. No animal died during and one week after the endoscopic procedure. Colonoscopy may safely performed in macaques. The images taken by colonoscopy may be important to establish diagnosis and treatment of colitis in macaques in time and to evaluate the efficacy of drug intervention as well. This technique is also helpful to provide qualified macaques for scientific researches.