Previous results have shown that the Bacillus subtilis clpP gene is required for developmental processes such as sporulation and competence development. Little is known about its function during the initiation of sporulation. We studied the effect of clpP mutation on the early events of sporulation. The expression of the spo0A and spoIIG genes, whose active transcription requires the phosphorylated Spo0A protein (Spo0A similar toP) as the transcription activator, was significantly decreased in the clpP mutant at the onset of sporulation. The expression of spo0H gene encoding sigma (H) protein was also greatly reduced. As expected from these results, the sigma (H) and Spo0A protein levels in the clpP mutant were also decreased during the initiation of sporulation, indicating that the accumulation of Spo0A similar toP was inhibited in the clpP mutant. We, therefore, introduced the mutation of the spo0E gene, which codes for the Spo0A similar toP-specific phosphatase, into the clpP mutant and found that this double mutant restored the expression of the spo0A as well as spoIIG genes. These results suggest that ClpP had an indirect influence on the intracellular concentration of Spo0A similar toP by regulating the activity of the Spo0E phosphatase during the initiation of sporulation.