The kinetics of alcoholic fermentation was evaluated using the following substrates: molasses, urea, and diamine phosphate (MUDP); molasses and guava seed flour (MGSF); and molasses and dry mycelium of Aspergillus niger (MMAN). The fermentations were done using Saccharomyces cerevisiae under anaerobic conditions, 32°C, and pH 4.6. For each fermentation substrate the effect of the nitrogen source on cell viability (V), substrate conversion (CS), ethanol yield (Y p/s ), and productivity was evaluated. The MGSF substrate showed the highest product yield (5.86 gg -1 ) and substrate conversion (47.58%) at 18 and 24 h of fermentation, respectively, with a maximum ethanol concentration of 60 gL -1 . Substrate MMAN showed a low ethanol yield (36 gL -1 ). It was concluded that guava seed flour is a viable and economic nitrogen source for alcoholic fermentations.