This study compared the effects of a bacterial inoculant (containing Lactiplantibacillus plantarum, Pediococcus pentosaceus, Enterococcus faecium) and a chemical preservative (formic acid, propionic acid, formates and benzoates) at two doses on fermentation quality and aerobic stability of alfalfa silage. Alfalfa with 37.3% dry matter was ensiled for 33 weeks with continuous temperature monitoring. The bacterial inoculant significantly reduced pH (4.12 vs. 4.16) and NH3-N content (27.6 vs. 28.1 mg N/100 g) compared to control. The chemical preservative more effectively controlled temperature during fermentation (peak 33.5-34.5oC after 7 weeks) compared to inoculant and control (38.7-39.7oC after 3-4 weeks). Higher doses of additives had no significant effect on fermentation quality. All variants showed good aerobic stability. The bacterial inoculant demonstrated better effects on fermentation parameters, while the chemical preservative more effectively controlled temperature. Properly preserved alfalfa silage showed good aerobic stability regardless of the type of additive used.