Six-weeks experimental trial was conducted to evaluate the effects of excess dietary threonine [Thr] (150% and 200% of NRC recommendations) with levels of 21% and 22% dietary protein on productive performance, blood biochemical parameters and small intestine histological structure of Japanese quail. Three hundred and fifteen one-day-old unsexed Japanese quail chicks were randomly assigned for seven experimental groups, 45 chicks each. T1- chicks were fed the basal (control) diet contained 24% crude protein; T2 and T3-birds were fed diets contained normal requirement of [Thr] with 22 and 21% crude protein, respectively; T4 and T5-quails received 22% crude protein with 150% or 200% [Thr], respectively; T6 and T7-were given 21% crude protein with 150% or 200% [Thr], respectively. The obtained results showed that [Thr] supplementations particularly 150%, improves quail productive performance and compensates dietary protein restriction. Plasma concentrations of total protein, albumin, high-density lipoprotein (HDL), and glucose were increased significantly (P<0.01), while triglycerides and low-density lipoprotein (LDL) were decreased with [Thr] dietary addition. Kidney and liver functions were not negatively influenced with [Thr] supplementation at any level. The histological observations of intestine showed greater villi height and higher goblet cells number with [Thr] supplementation indicating better digestibility and utilization of feed nutrients. It could be concluded that, supplementary [Thr] at 150% of basal requirement of broiler quails was sufficient to compensate for reduction of dietary crude protein below the NRC recommendations, the therefore, [Thr] supplement had no adverse effect on kidneys and liver functions and improved intestinal status, structure and functions.