Social support plays a vital role in the health of HIV/AIDS patients, but there needs to be a validated instrument to measure social support in Vietnam. This cross-sectional study was to validate a Vietnamese translation of the Multidimensional Perceived Social Support Scale (MSPSS). The study had three stages: [1] translation to Vietnamese, [2] pilot testing, and [3] validation of the translation. Stage 1, including forward and backward translation by four independent translators, resulted in a good content validity translation. Pilot testing was done on 30 HIV/AIDS patients: the translation was understandable, and no change was required. Five hundred HIV/AIDS patients were recruited in stage 3. The translation had excellent internal consistency (Cronbach’s alpha: 0.90), good test-retest reliability (intra-class correlation coefficient: 0.95), and good concurrent validity. Construct validity was well established by confirmatory factor analysis. The Vietnamese translation of the MSPSS is reliable and valuable for measuring perceived social support.