Chitosan nanoparticles were studied as antimicrobial agent. The antibacterial activity of chitosannanoparticles were investigated against three Gram-negative bacteria; Escherichia coli,Pseudomonas aeruginosa and Salmonella typhi, and three Gram-positive bacteria; Staphylococcusaureus, Enterococcus faecalis and Streptococcus pyogenes. The antifungal activity were examinedagainst three fungi; Geotrichum candidum, Candida krusei and Candida parapsilosis.The antiviral activities were tested against three viruses; Rift Valley Fever (RVFV), Herpes simplex-1 (HSV-1) and Coxsackie viruses. Chitosan nanoparticles were inhibited all bacteria andfungi except E. faecalis seemed to be resistant strain. Infectivity titers of all viruses were reducedby chitosan nanoparticles, which are a natural antimicrobial agent.