Solvent - antisolvent recrystallization employed for size reduction of HNS has been described and the effect of various parameters such as stirring rate, effect of antisolvent type, antisolvent temperature, ultrasonication, etc. was investigated. Purified HNS, produced by hot solvent recrystallization of production grade crude HNS, of mean particle size 95 am was used for preparation of ultrafine particles of HNS. Solvent contamination in terms of residual solvent was determined by (1)H NMR and GC-MS analysis. In addition, ultrafine HNS has been characterized for purity (HPLC, (1)H NMR), particle size and shape (PSA and SEM), specific surface area (BET analysis), thermal behavior (TGA, DSC), sensitivity (impact, friction), etc. The results have been compared with C-HNS. UF-HNS was >99% pure with mean particle size <1 mu m. SEM showed submicrometer size rods like particles of HNS as the final material.