Selenium nanoparticles (SeNPs) with diameter of similar to 74 nm were synthesized by gamma Co-60 ray irradiation of H2SeO3/dextran solution. The SeNPs were characterized by UV Vis spectroscopy spectrum and transmission electron microscope (TEM) images. The effect of pH of H2SeO3/dextran solutions before gamma irradiation on the size of SeNPs was investigated. The SeNPs/dextran powder was also prepared by spray drying technique and the purity was verified by energy dispersive X-ray (EDX) analysis. The ATBS(center dot+) radical scavenging ability and reducing power of SeNPs were assessed. Results showed that SeNPs/dextran with concentration of 25-100 ppm exhibited high antioxidant activity. The as-prepared SeNPs/dextran powder with selenium content of similar to 2.51% (wt%) was of high purity. The influence of gamma Co-60 ray sterilization at dose of 25 kGy on the characteristics of SeNPs/dextran powder was also examined. (C) 2017 Elsevier B.V. All rights reserved.