We investigated the effect of inoculant on the emission of odorous compounds during isothermal thermophilic composting processes at 60degreesC. Of these compounds, ammonia and odorous sulfur compounds, hydrogen sulfide (H2S), methylmercaptane (MMC), dimethylsulfide (DMS), and dimethyldisulfide (DMDS) were measured. We used three different inoculants, and found that composting with two of them, where vigorous organic matter decomposition occurred, generated a very high concentration of NH3, as high as 4000 ppm, and also generated high concentrations of sulfur compounds, especially of MMC and DMDS. In contrast, very few odorous compounds were emitted during composting with the third inoculant; however, there was an extremely small degree of organic matter decomposition in this composting. These results indicate that it is not sufficient to merely compare odor emission when assessing the best operational conditions for composting with a small amount of odor emission. In other words, in assessing composting operations with regards to the effective reduction of odor emissions, it is important to simultaneously quantify the degree of organic matter decomposition that occurs.