Since composting is the decomposition process of organic materials by microorganisms, the quality and the quantity of odor emissions should be influenced by the types of microorganisms which decompose the organic materials. This study, examined the effect of seeding on the emission of ammonia, one of the most troublesome components of the odor produced by composting. When three different commercially available seeds were tested for composting the time courses of organic matter decomposition and ammonia emission differed among them, but the quantities of ammonia emitted were simlar when the same quantity of organic material was decomposed and no remarkable difference in the effect of ammonia reduction was found among them. A thermophilic bacterium, Bacillus licheniformis DO 1, was then obtained from compost as a potentially effective thermophilic microorganism for reduction of ammonia emissions during composting, which grew on protein-contaning medium without greatly increasing the medium pH. When this strain was used as a seed for composting at the optimum temperature of 50degreesC, ammonia emissions were reduced to about 40% of those observed with the commercially available seeds.