Abstract : Twenty four individual Awassi lambs (weighing  26.5 kg ± 1.1 and 5 months ) were used to study biochemical changes in rumen parameters as affected by feeding diets containing different levels of dietary crude protein (low, medium and high- CP) formulated with high and low rumen degradable to undegradable dietary nitrogen ratios(RDN:UDN). Blood samples were withdrawn from lambs before feeding (0 times), 3 and 6 hrs post feeding. Results revealed that blood glucose concentration (BG) and blood total protein (BTP) were significantly increased (P<0.05) due to feeding low RDN:UDN ratio but not due to increasing level of dietary protein. However, blood urea nitrogen (BUN) concentration was significantly increased (P<0.01) due to both factors. Result of interaction showed that better blood parameters were detected in blood samples withdrawn from lambs fed low RDN: UDN ratio. Higher BG concentrations were detected when low and medium levels of CP. Higher BTP concentrations were detected when medium and high levels of CP were offered with this ratio.  In conclusion high and low ratios of RDN:UDN improved the utilization of medium level of dietary protein in comparison to high level as evidenced by blood urea nitrogen concentrations. Keywords: Protein, degradability, blood parameters, lambs