Black soybean (Glycine max (L.) Merr) is one of the varieties from soybean that has been used for centuries as health promotor foods and one of the way to utilize it by fermentation. Fermentation could increase the antioxidants activity and reduce the off-flavor of black soybean. In this study, black soybeans were processed into soy yogurt using culture of Lactobacillus bulgaricus and Streptococcus thermophilus with two stages of research. The first stage determined the concentration of skim milk to be used 5, 10, and 15% and view its effect on pH, total tirated acids (TAT) value, total BAL, and viscosity according to existing standards. The second stage study was continued by looking at the effect of culture ratio (1:1, 1:2, and 2:1) and fermentation time (14, 16, and 18 hours) to antioxidant activity. Antioxidant activity was calculated using DPPH method and got the best result at culture ratio of 1:1 with 14 hours fermentation time of 27.228,54 ppm. The selected formulation was followed by a total phenolic test (1,66 mg GAE/g yogurt) and flavonoids (0,55 mg quercetin/g yogurt), hedonic test, and proximate analysis.