The morphological and biochemical characters and effect of a highly protein diet on Japanese quail were investigated. Total participants in this study were twenty adult male and eighteen female Japanese quail, they were at three different old-stages; 30-days, 90-day and 180-day old. They were offered highly-protein food and water for two weeks. After two weeks, the serum has been centrifugated, hence different indicators including the total protein were assessed. Kidneys were examined with a light microscopy, their masses were estimated. Data analysis was performed using SPSS-22. we observed a decrease in width of middle lobe of kidneys in 90-days old quail birds (22%) and 180-days old quail birds (18%). The perimeter of anterior lobe has been increasing as the age increases, whereas it was a decrease in the middle lobe (35%) and posterior lobe (31%) in 90-days old quail birds. As compared between sex-based groups, it has been shown increase in absolute value of kidney weight among 90-days old (23%) and in 90-days old (7%) female quail birds. Absolute mass has been found more in left kidney at 30-days old (16%) and lower in the right kidney in all age groups female quail birds than that of males. A decrease in length of three lobes of the kidneys was observed in 180-days old females of quail birds (20%), whereas it has been found significantly increase in the width of front lobe (11%) in females quail birds. There was an increase in the amount of general protein and level of albumin in females and males in all age groups. The globin was higher in males than was in females. When comparing the ratio of phosphorus and calcium, it was observed that both of them were higher in females than males. Alkaline phosphate and hemoglobin were elevated in males in 180-days old. © 2021, Islamic Azad University. All rights reserved.