Abstract. Research on soy milk kefir on the growth of Propionibacterium acne has been carried out by the Laboratorynof Milk Processing SciencenandnTechnology Animal Husbandry Study Program, Faculty of Agriculture,nUniversitynofnSyiahnKualanBandanAceh, which was held from December 2018 to January 2019. This research uses a Completely Randomized Design (CRD) consisting with 3 (three) treatments and 6 (six) replications to obtain 18 samples. The antibacterial activity of soy milk kefir on the growth of Propionibacterium acne is an active compound produced during fermentation which is able to inhibit the bacteria Propionibacterium acne by protein content and cynesis, which has a significant effect. The aim of this studynwasntondeterminenthenantibacterial ability of soy milk kefir to the growth of Propionibacterium acne. The problem statement whether adding kefir seeds to soy milk has an effect on the antibacterial ability of Propionibacterium acne. The research data obtained were analyzed statistically by Analysis of Variance ANOVA. If there is an influence, then proceed withnthenSmallestnSignificantnDifferencenTest (LSD). Based on the results of data analysis, the starter level of 5% kefir seeds produced soy milk kefir with a high protein content of 4.70 and the lowest syneresis was 9.02%. While the best area of inhibition zone is obtained at the starter level of 2.5%, which is indicated by the area of inhibition zone on the 5.83 mm whey component and the casein component has an area of 5.58 mm inhibition zone. Basednonnthenresultsnofndatananalysisnit cannbe concluded that the use of a 2.5% starter level is recommended for cosmetic product preparations as indicated by the ability of whey and casein components to inhibit the growth of Propionibacterium acne and to be economically optimal in the use of kefir seeds. Keyword: Antibacterial, P. acne, Soy Kefir