Rice straw (Rs) was treated by a sodium chlorite/acetic acid mixture (Sct), ammoniation (At) and alkaline hydrogen peroxide (Athp) methods. The objective was to compare their degradation and fermentation products in the presence or suppression of anaerobic fungi. Significant differences (P At > Rs > Athp. Suppressing fungal activity with cycloheximide resulted in a decrease in dry matter degradation, with concomitant decrease in total volatile fatty-acid concentration. While the suppression of fungal activity with cycloheximide depressed acetate and butyrate production, it favored an increase in propionate production.