According to the International Dairy Federation, fermented milk is the product elaborated from milk, skimmed or otherwise, using specific lactic cultures, which are maintained alive until acquisition by the consumer, and are not pathogenic. The aim of this work was to develop a fermented soy drink inoculated with a lactic culture as Lactobacillus casei and observe the final viable cell count. A water soluble soybean extract was used, in which the formulations established in this research were reconstituted in 10% water pre-heated to Ta = 35ºC to facilitate homogenization. The homogenization process was carried out using an industrial blender, one liter being prepared for each formulation. Different carbohydrate concentrations (100% sucrose, 100% glucose, 50% glucose, 50% sucrose and 0% sugar) were used to evaluate the fermentation of a soluble soy extract using lactic starter as Lactobacillus casei. Formulations A1 and A2 (no supplementation and supplemented with sucrose) presented the shortest fermentation time, of approximately 11 hours. On the other hand formulation A3 (supplemented with 50% sucrose and 50% glucose) required more than 12 hours, and formulation A4, containing glucose, took more than 13 hours. Since the inoculum of L. casei was a pure culture, fermentations using this culture took longer time to reach the ideal pH value for a fermented milk. The lactic bacterial counts were above 1 x 1011 at the end of storage. Soy was shown to be an optimum medium for the development of the desired lactic culture, the carbohydrates stachyose and raffinose were available for fermentation.