The invention discloses an application of 
Ag nanoparticles to preparation of medicines for restraining 
nosema bombycis as a main 
pathogen of 
bombyx mori. The 
Ag nanoparticles are spherical, are 3-24nmin dimension and are 0.23nm in 
crystal lattice distance. Through Ag 
nanoparticle solution of different concentrations, the 
toxicity of 
bombyx mori larvae is tested, and the result shows that the weight, the cocoon shell rate and the oviposition number of the 
bombyx mori larvae between groups do not have significant differences, which indicates that the Ag 
nanoparticle solution having the concentration being 100 [mu]g / mL or below is safe to the 
bombyx mori larvae; a mechanism of 
Ag nanoparticles for resisting 
nosema bombycis is analyzed, then the inventor finds that the Ag nanoparticles can seriously destroy the structure of the 
nosema bombycis, when the Ag nanoparticles act with 
spore coats, the permeability is increased, so that some substances of 
DNA, proteins and the like are destroyed, the 
infestation capacity is greatly reduced, the pathogenic capacity of the nosema bombycis is reduced, and the disinfection effects of the nosema bombycis can be achieved; and the Ag nanoparticleshave important significance in controlling the nosema bombycis of the 
bombyx mori.