Background: Intestinal parasitic infections are still very common, especially in areas where immune-compromised patients like HIV/AIDS patients are high prevalent. Therefore, the aim of this study was to assess the prevalence of intestinal parasite and risk factor among HIV/ AIDS patients attending ART clinic in Mizan-Tepi university teaching hospital, Southwest Ethiopia. Method: A cross -sectional survey was conducted from July to September, 2021. A total of 191 study subjects were participated in this study. A structured questionnaire was used for collecting socio-demographic and risk factors data. Stool sample was collected and processed using direct wet mount, formol-ether concentration technique and modified Ziehl-Neelson staining techniques. Data was analyzed using statistical package for social sciences (SPSS) Version 25 software and logistic regressions were applied to assess any association between explanatory factors and outcome variables. Result: From a total of 191 stool samples, 67 (35.1%) were positive for intestinal parasites. The prevalence of intestinal parasites among patients on-ART was 31.5% (45/143) and 45.8% (22/48) among ART naïve group. Entamoeba histolytica/dispar (7.7%) and (12.5%) and Giardia lamblia (7.0%) and (10.4%) was the most predominant parasites detected both in ART and ART naïve groups (p > 0.05). Drinking untreated water (AOR = 0.13; 95% CI: 0.016-1.012), consuming raw food (AOR = 0.23; 95% CI: 0.025-2.108), eating unwashed raw vegetables (AOR = 2.26; 95% CI: 1.052-4.843); CD4 count <200cells/ mm3 (AOR = 0.22; 95% CI: 0.062-0.798), CD4 count 200-500cells/mm3 (AOR = 0.40; 95% CI: 0.195-0.811), WHO stage II (AOR = 0.30; 95% CI: 0.156-0.589), WHO stage III (AOR = 0.32; 95% CI: 0.108-0.917) and viral load ≥150 copies/ml (AOR = 0.44; 95% CI: 0.220-0.873) were showed significant association with prevalence of intestinal parasite.Conclusion: In this study, higher rate of intestinal parasitosis were associated with hygienic practices like drinking untreated water, consuming raw food and eating unwashed raw vegetables and with some clinical findings such as lower CD4 counts, increased viral load and being WHO stage II & III. Therefore, public health measures and adherence to ART should be strengthened to improve the immune status and to reducing vulnerability of the patients for intestinal parasites.