The present invention provides a redispersible powder and aqueous dispersions of nanoparticles of water insoluble organic pesticides. The invention further provides methods for preparing the redispersible powder and the aqueous dispersion, wherein the methods include preparation of an oil-in-water nanoemulsion or microemulsion and solvent removal. The present invention also provides pesticidal compositions of the redispersible powder or aqueous dispersions, and their agricultural use in combating pests.