Background and rationale: : Human immunodeficiency virus (HIV) is a major public health problem in all countries around the world, having claimed 36,3 million lives so far. Lao PDR. HIV has been increasing among key populations, particularly men who have sex with men (MSM). According to the 2017 Integrated Biological and Behavioral Surveillance (IBBS), the prevalence rate of HIV among MSM in Vientiane Capital has increased from 2.8% in 2014 to 7% in 2017. Objective: : This study aimed to identify the factors associated with HIV infection among men who have sex with men in Vientiane capital of Lao PDR. Methodology: : This study was a matched cases-controls study in a sample of 192 men who have sex with men registered with a positive HIV test result (Case) in Mahosot Hospital, Setthathirat Hospital, and Mittaphab Hospital and those with a negative HIV test result (Control) in Vientiane Capital. With a 1:1 ratio of 96 cases and 96 controls, with matched sexual roles (intimate or penetration, receptive, both intimate and receptive) using a purposive sampling method. Data collection was done using a face-to-face interview form with informed consent from the interviewees. All data were entered into the Epi-data program and transferred to the STATA program for data analysis. Results: : Out of 192 participants, the mean age for all participants is 27.2(+5.7) years; 69.8% of cases and 59.4% of controls are in the age group of ≥ 25 years old. The marital status for both groups most 94.8% were single. 45.9% of cases and 69.8% of controls had the higher education or equivalent to the diploma level. Cases were more likely than controls to have had a monthly income of >1,600,000 (56.2% vs. 40.6 %). Factors associated with HIV infection were monthly income of >1,600,000 (AOR=2.4; 95%CI=1.0-5.0; P-value=0.040), low knowledge of HIV (AOR=4.8; 95%CI= 1.9-11.9; P-value=0.001), bisexual (AOR=4.6; 95%CI= 1.2-17.1; P-value= 0.019), not always using condoms with male casual partners (AOR=14.7; 95%CI= 5.3-40.8; P-value<0.001), ever sexual behavior stigma (AOR=3.1; 95%CI= 1.2-8.1; P-value=0.015) and not interested PrEP (AOR=10.5; 95%CI= 4.1-26.8; P-value<0.001). Conclusion: The findings of the factors associated with HIV infection, which including of monthly income, knowledge of HIV, sexual preference, condom used, feeling of stigma regarding to sexual behavior, and access to PrEP. This study will provide the information for action plans and the development HIV prevention activities among MSM. There should be promoting condom used, accessing to PrEP, and HIV prevention information in order to reduce the new HIV infection cases.