Abstract: The effect of microbial and chemical additives on the quality of alfalfa silage were tested in this study. Alfalfa was harvested at budding and early-flowering stage and wilted to approximately 70% moisture content and treated with four additive treatments; distilled water (control), 10⁵ cfu/g Lactobacillus plantarum and 50 mg/kg cellulase (LP+C50), 10⁵ cfu/g L. plantarum and 100 mg/kg cellulose (LP+C₁₀₀) and 6 mL/kg formic acid+propionic acid (FA+PRA), with 3 replications. Silages were analyzed after 30 d of ensiling. This study indicated that alfalfa harvested at the early flowering stage had lower pH (P<0.05), butyric acid (BA) and NH< sub >3-N (P<0.01) than those harvested at budding with significantly less non-protein nitrogen (PA) and unusable protein (P<0.01). All three additives significantly increased the fermentation quality of alfalfa by decreasing the pH and content of NH₃-N (P<0.01). Alfalfa silage treated with LP+C had significantly higher lactic acid and lactic acid/acetic acid (P<0.01) while BA was not detected in the FA+PRA treatment. All additives had higher water soluble carbohydrate (WSC) and crude protein (CP) and less neutral detergent fiber (NDF) and acid detergent fiber (ADF) (P<0.01) than the control. Applying LP+C₁₀₀ and FA+PRA markedly decreased the concentration of non-protein nitrogen and unusable protein, and increased the content of true protein in silages (P<0.01). The results suggest that alfalfa silage treated with FA+PRA had the highest quality, followed by LP+C₁₀₀ treated silage.