Abstract: The ensiling of Italian ryegrass (Lolium multiflorum) silage was carried out under laboratory conditions and propionic acid was added to give a series of different concentrations (0, 0.20%, 0.25% and 0.30%) to investigate the effect on dynamic changes in the fermentation process. Adding propionic acid to the L. multiflorum silage did not influence the VFAs during ensiling, but increased the lactic acid, WSC and LA/AA at the late stages of ensiling. The propionic acid additive decreased lactic acid and the pH value during the early stages of the fermentation. The AN/TN value and acetic acid content were also decreased in the silage. The propionic acid content was always high during the whole process of ensiling. These Results suggest that adding propionic acid to the silage at a rate of 0.25% is the optimum for fermentation quality of L. multiflorum.