Interest in soybeans and soy-based products has grown significantly in the last decades due to their reported nutritional and health-promoting effects. In soybean and non-fermented soy foods, isoflavones are predominantly found as glucosides, which must be hydrolyzed in order to exert their documented beneficial effects. The objective of this study was to evaluate the effect of soymilk fermented with Lactobacillus rhamnosus CRL981, a strain that can completely hydrolyze glucoside isoflavones due to its high beta-glucosidase activity. Using a diabetes animal model induced with streptozotocin, it was shown that the fermented soymilk was able to significantly decrease glucose levels, total cholesterol concentrations, triacylglycerols and increase antioxidant enzyme activities compared to animals that received unfermented soymilk. This study clearly shows that the adequate selection of starter cultures could be used to develop novel soy based products intended for the prevention or adjuvant treatment of diseases such as diabetes.