This trial assessed the impacts of reducing crude protein (CP) by 1.5% with a high lysine amino acid profile, and adding 5% sunflower meal on broiler chickens' growth, intestinal histomorphology, serum biochemical parameters, and carcass traits. Six treatments (T1 to T6) of three hundred and sixty-day old ROSS 308 chicks were classified into completely random system, with 6 replicates of ten chicks per replicate. Sunflower meal was included at 5% in all groups except the control (T1). The diets were designed to provide the lysine recommended level (100%) for T1 and T2, and increased lysine levels (105%, 110%, 115%, and 120%) for T3 to T6, with the amino acid profile adjusted accordingly. The results revealed no significant variations (p > 0.05) in final BW, BWG, feed intake, and FCR. The results of liver, gizzard, abdominal fat, intestine, spleen, and heart percentages also showed non-significant differences. However, the weight of the bursa recorded high (p < 0.05) significant results in treatment T6. The results of total cholesterol were significantly decreased in T5 compared to other treatments, while HDL-C levels were highest in T2. Albumin levels were highest in T5, while AST levels were highest in T1 and lowest in T6. Uric acid and urea levels varied significantly, with T1 showing the highest levels. Groups T5 and T6 exhibited significantly wider and longer villi, deeper crypts in the duodenum, in addition to longer villus in the ileum. There were no significant variations in the villi length to crypt depth ratio. Overall, the dietary interventions had no negative impact on broiler performance, serum parameters and intestinal health.