This study investigated the changes in chemical composition of cassava and sweet potato flours during 72h of solid-state fermentation process using baker’s yeast Saccharomyces cerevisiae as fermentation factor. Both cassava and sweet potato flours were mixed with distilled water to reach 50% moisture content, before being inoculated with 2% of activated yeast solution in solid-state fermentation conditions for 72h at room temperature. Fermented samples were taken at 24h intervals to measure the changes in pH values and yeast population. Samples were then dried at 55oC in a convection oven and the products were analyzed for proximate composition. The results showed a reduction in the pH values and an increase in the microbial count during fermentation, particularly within 48h from starting point. The highest number of yeast cells was observed at 48h (4.79 and 5.06 107CFU/g, respectively in the fermented cassava and sweet potato), leading to an efficient increase in the protein and reduction in the fiber contents of the two substrates. Particularly, remarkable changes in protein and fiber levels were higher in the cassava samples compared to the sweet potato samples. Therefore, the cassava fermented product, harvested at 48h of the fermentation has the potential to be used as functional feed additives in animal diets.