The present study was conducted to evaluate the effectiveness of mebendazole in the treatment of Hymenolepis nana infection in ring-tailed lemurs (Lemur catta). Ten (L. catta) from the Chengdu Zoological Garden in China, which were naturally infected with H. nana, were treated with mebendazole (10 mg/kg for 5 days). A posttreatment fecal examination was conducted 10 and 20 days after the start of treatment. All treatments resulted in a decrease in the number of eggs per gram in the posttreatment sample compared with the pretreatment sample. Reduction of mean egg count was 97.6% and 100% on days 10 and 20, respectively. The results indicated that mebendazole has marked efficacy against H. nana infections in L. catta.