Iron has a crucial role in growth as part of metalo-proteins like haemoglobin or myoglobin, enzymes; they are also involved in energetic reactions. Iron plays a vital role in fertility. At high doses, Iron has a harmful consequence on the reproductive system, which can be strongly reflected the final stage of spermatogenesis. Nutritional products are claiming to use nanotechnology and it is important to recognize the potential toxicity of nano-sized nutrients. Recently iron nanoparticles were proposed as a food additive for poultry. The objective of this study was to investigate the effects of L-cystein coated iron oxide nanoparticles on reproductive performance in male quails. The results of Fourier Transform Infrared Spectrometer, Alternating Gradient Force Magnetometer and Scaning Electron Microscopy showed that iron oxide nanoparticles was produced and have been coated with L-cycstein (Fe3O4-Cys NPs). A total of 100 one-week-old quail chicks were randomly placed to five groups of five replicates. Four quails (two male and two females) were raised in an individual cage for each replicate. The five experimental treatment diets consisted; negative control diet, with no Iron supplementation; positive control diet supplemented with 60 mg/kg of Fe3O4; treatment diets supplemented with 0.6, 6 and 60 mg/kg of L-cystein coated iron oxide nanoparticles. The hemoglobin, Red blood cell, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, gonadal somatic index, daily sperm production, total testicular sperm and sperm viability of the male quails that were fed with diet supplemented by 0.6 mg/kg of Fe3O4-Cys NPs were improved as compare with negative control. This study showed that not only the use of the Fe3O4-Cys nanoparticles had no side effects but also it can be used as a feed additive to improve the reproductive performance in male quails.