Selenium nanoparticles (Se-NPs) have gained importance in poultry due to their ability to improve growth performance, bioavailability and digestive efficiency compared to inorganic sodium selenite (SS). This study compared the effects of selenium nanoparticles and inorganic sodium selenite on growth performance, nutrient digestibility, and serum biochemical parameters in Japanese quails. A total of 420 quails (14 days old) were distributed into five groups having 84 birds in triplicate, 1^st group as control, fed by basal diet; 2^nd and 3^rd group were supplemented with Se-NPs (0.2 mg/ kg and 0.4 mg/ kg), 4^th and 5^th groups were fed with SS (0.2 mg/kg and 0.4 mg/kg), respectively. By using these two levels of supplementation, the study assessed a dose-response relationship, helping to identify any benefits or adverse effects associated with increasing selenium levels. The results showed that quails fed with Se-NPs (0.4 mg/kg) had higher body weight and enhanced digestibility of dry matter, organic matter, crude protein, crude fiber, ether extract, and ash content. Glucose, protein, cholesterol, triglycerides, HDL, and LDL concentrations were significantly lowered (P < 0.05) in the quails fed with Se-NPs (0.4 mg/kg). The concentration of hemoglobin, WBCs, platelet count and neutrophil were higher (P < 0.05) in the group treated with Se-NPs (0.2mg/kg). This study underscored a dose- response relationship, demonstrating that higher levels of Se-NPs (0.4mg/kg) corresponded to improved growth and metabolic outcomes. In conclusion the result indicated that feeding the quails with Se-NPs (0.4mg/kg) enhanced their growth performance, nutrient digestibility and lowered the cholesterol, triglycerides, HDL, and LDL level in comparison to the SS diet.