A study on the screening and isolation of microorganism was performed for the removal of main malodor, such as ammonia, produced from the livestock farm. The main malodor components in livestock farm are ammonia, volatile fatty acids, sulfur compounds and trimethylamine. Damages to man and livestock were originated from malodors mainly due to ammonia, and thus ammonia reduction experiments were performed. Sludge of sewage treatment plant was inoculated in the sesame dregs culture, from which ammonia gas was produced. An aerobically grown, pure cultured isolated from the 10th enrichment culture was analyzed by 16S rRNA sequencing and identified as Alcaligenes sp. NS-1. This strain NS-1 precultured in the sesame dregs was found to remove ammonia gas with an efficiency of approximately 99-100% at an average concentration of 40 ppmv of ammonia gas. When the strain NS-1 sprayed to pig excrements, the removal efficiency at an average concentration of 100 ppmv of ammonia was approximately 60% after 16 hr.