Fermentation of plant substrates can be used to produce beverages with better functional properties. Saccharomyces boulardii is a probiotic that has robust fermentative properties related to its genus, but some fermentation factors must be carefully adjusted as they can affect the physico-chemical and biological properties of the products. In this sense, an experimental design was applied to evaluate the impact of agitation (rpm) and initial inoculum on yeast growth and on the antioxidant and antidiabetic properties of a functional beverage produced using a binary mixture of lentil grains and brown rice fermented for 24 hours at 30°C. Cell growth was assessed by drop-plate counting method; the in vitro antioxidant potential was evaluated by DPPH- and ABTS-radical scavenging activities and ferric antioxidant power (FRAP) assays; and the antidiabetic potential was investigated by evaluating the inhibition of the α-amylase enzyme activity. According to the conditions used in the process, viable cell counts ranged from 9.67 to 10.40 log CFU/mL. The antioxidant potential values measured by the ABTS method ranged from 1245.91 to 1352.57 µmol TE/mL, while the values obtained for the DPPH and FRAP methods ranged between 495.54 and 537.48 and from 345.41 to 437.64 µmol TE/mL, respectively. The maximum α-amylase inhibition reached was 39.57 %. The effects of the factors were statistically significant (p-value < 0.05) for microbial growth and for antidiabetic potential; the agitation effect was negative, and the initial inoculum was positive. On the other hand, for antioxidant properties, the studied factors on the range evaluated did not demonstrate statistically significant effects (p-value > 0.05). The results obtained allowed to conclude that the process developed to produce fermented beverages using lentil and brown rice grains can be carried out in a wide range of agitation and initial inoculum levels without negatively affecting the biological properties of the final product.