The temporal and spatial distribution of the genus Bacillus and Clostridium histolyticum group in swine manure composting was determined by fluorescent in situ hybridization using fluorescently labeled 16S rRNA-targeted oligonucleotide probes LGC353b and Chis150, respectively. The temporal distribution of total bacteria, Bacillus and C. histolyticum, detected in each layer of the composting pile was noticeable in that the number of them detected at the high-temperature stage was higher than that of the cooling stage. The number detected at the cooling stage was higher than that of the temperature-rising stage. The number of the total bacteria distributed in three locations achieved balance at the stage of cooling. The spatial distribution of the genus Bacillus cells was that the number and the relative abundance of Bacillus cells detected in the middle layer of composting pile were the lowest at each stage of composting. However, the minimum value of the relative abundance exceeded 8%. Compared with Bacillus spp., the C. histolyticum group displayed higher relative abundance in the same layer at different stages of composting except in the top layer at the stage of high temperature. However, the characteristic of the spatial distribution was not noticeable. The detected limits of the genus Bacillus and C. histolyticum group were both found to be the high cell density of 10(6) cells g(-1) (wet weight). These results indicated that the genus Bacillus and C. histolyticum group were the predominant bacteria in the swine manure composting process and may play important role in this complex environment.