A 2 x 3 factorial study examined some ileal morphology and blood biochemical parameters of broiler chickens fed diets containing graded levels of crude protein with or without guanidino acetic acid (GAA). Six diets containing two levels of crude protein (standard levels 23.01, 21.01, 19.04% or low levels 21.00, 19.03, 17.07%) in the starter, grower and finisher respectively supplemented with three levels (0.0, 0.06 or 0.12%) of GAA were used. Each treatment was randomly assigned to 6 replicates (10 male Hubbard broiler chicks per replicates). The results indicated that: Some ileal morphology (Chicken fed standard diets have significantly (P<0.05) taller Villi height (1269 µm) than those fed low protein (-2% CP) diet (1140, µm). In addition, significant differences were observed in Villi height values between chickens fed (0.0% GAA) diets and those fed (0.06 and 0.12% GAA) diets (1125, 1271 and  1217 m) respectively, while, no significant differences were observed in villi width or crypt depth (m) among all treatments), and Some blood parameters (Dietary CP level (standard vs.-2 CP) and GAA supplementation level (0.0, 0.06 and 0.12%) had a significant effect on all blood plasma parameters, examined herein, including levels of total protein, albumin, glubulin, A/G ratio, total lipid, triglyceride and cholesterol.  On the other hand, chicks fed low protein diets (-2%CP) and (0.0% GAA) have significantly higher values of total plasma lipid, cholesterol and triglycerides)