Red clover (Trifolium pratense L.) and alfalfa (Medicago sativa L.) herbage were harvested, ensiled into laboratory silos and opened after 1,2,3,7,10,15 and 35 d of storage. The pH and nitrogen distribution were detected in all ensiling stages. The results showed that red clover silage have significant lower pH than alfalfa silage at every stage of ensiling. The non-protein N (NPN) concentration of these two forages kept increasing along with the ensiling processing and red clover silage has significant lower accumulation of NPN than alfalfa throughout the whole fermentation. Similar trends were displayed in the concentrations of ammonia N (NH₃-N) and free amino acid N (FAA-N). Peptide-N exhibited rapid increase at the first few days, followed by decline and then increased again.