Searching for protein sources for fish diet formulations has become essential. So, this investigation evaluated the impacts of kidney bean protein hydrolysate (KPH) (Phaseolus vulgaris L) as a new plant protein source in the diets of Nile tilapia, Oreochromis niloticus (O. niloticus), on the fish growth, hematology, biochemistry, antioxidant status, and tissue histomorphology. Two hundred fingerlings (37.38 ± 0.058 g) were allocated to five experimental treatments (TRTs) in 20 glass tanks for a feeding trial of about 70 days. KPH was supplemented to the diets by five levels: 0, 5, 10, 15, or 20%. A linear increase in the fish growth was observed by dietary KPH supplementation. The final body weight was increased by 6, 12, 15, and 18% for KPH5, KPH10, KPH15, and KPH20, respectively. The red blood cells, hemoglobin, and packed cell volume were increased in the KPH15 and KPH20 groups compared to the KPH0 group. The serum TP and β2-globulin levels were increased in KPH-supplemented TRTs (P < 0.05). Reduced serum MDA levels and increased SOD activity were observed in KPH15 and KPH20 groups (P < 0.01). The best intestinal histomorphometry was seen in the KPH15 group. Histological analysis of the treated groups’ liver and kidney sections revealed a comparatively normal histomorphology. Splenic tissues of the treated groups were normal, with more prevalent lymphoid elements, especially in the KPH10 and KPH15 groups. In conclusion, KPH could be a potential source of protein in Nile tilapia diets with good results for fish growth, blood biochemistry, and antioxidant status. KPH supplementation had no adverse effects on fish organs. The recommended inclusion level was 15% of the diet.