This study aims to obtain isoflavones aglycone as genistein form through the process of fermentation of soybean by probiotic bacteria producing ß-glucosidase namely Lactobacillus acidophilus. Isoflavone aglycone obtained then testing the activity of osteoblast cell proliferation in vitro by MTT method that will be read by ELISA. Fermented in the extraction with ethyl acetate. Liquid extract was evaporated with a rotary evaporator and lyophilized by freeze dryer. Extract 3 mg in 10 ml of 80% methanol in UFLC analyzed its genistein levels. Comparators are used genistein standard ≥ 98% at concentrations of 5, 10, 15, 20, 25 ppm. The analysis of three replicate showed average levels of genistein 3.46%. The test results showed cell percent proliferation was highest at 0.5% extract is equal to 143.93%. Statistical analysis by ANOVA showed that H0 rejected, which indicates that there is the effect of the addition of fermented extract on cell proliferation of osteoblasts.