Soy milks prepared from full-fat soy flour, defatted soy flow, soy protein concentrate (SPC) and soy protein isolate (SPI) were fermented with Lactobacillus acidophilus. Effects of lactic fermentation on the flavor and volatile compounds of soy milks were investigated. Sensory evaluation showed that the flavor of soy yogurt beverages was inferior to that of milk yogurt beverage and the flavor of SPI-yogurt beverage was better than that of other soy yogurt beverages. SPI-milk fermented with L. acidophilus was more acceptable than unfermented SPI-milk. Lactic fermentation reduced n-hexanal in SPC-milk and SPI-milk while it increased diacetyl in both soy milks.