The objective of this study was to investigate the effects of cut and irrigation water quality on chemical composition and in situ dry matter (DM), crude protein (CP) and neutral detergent fiber (NDF) degradabil-ity of alfalfa. Three fistulated Zel sheep (approximately 2 years old) were used in a complete randomized design to evaluate the in situ RUMEN DEGRADABILITY. Ruminal incubation times consisted of 0, 3, 6, 9, 12, 24, 48, and 72 h. The results showed that increasing the cut of maturity and irrigation with saline water significantly cause to increase the components of cell wall (P=0. 0011) and decrease the protein concentrations in alfalfa (P=0. 0001). Except the quickly RUMEN DEGRADABILITY of DM that in first cut of alfalfa was higher, other parameters of ruminal DEGRADABILITY of DM were not different. Ruminal NDF DEGRADABILITY in second cut of alfalfa, that irrigated with saline water, was higher (P=0. 0143). Degradation rate of NDF in first cut of alfalfa, and effective RUMEN degradation of NDF at different passage rate in alfalfa that irrigated with saline water were higher. Slowly ruminal CP DEGRADABILITY (P=0. 001) and effective degradation at different passage rate of alfalfa, that irrigated with saline water, were higher. The cut did not effect on CP DEGRADABILITY of alfalfa. Our experiment indicates that increasing water salinity have not a negative effect on alfalfa forage quality.