A 2.8kb DNA fragment including whiB-like gene was cloned from the partial DNA library of Streptomyces ansochromogenes 7100 by using whiB of Streptomyces coelicolor J1501 as a probe. The nucleotide sequence of 1.4kb DNA fragment was determined and analyzed. The result showed that the fragment contains one complete open reading frame-designated sawE. sawE shows strong identity to whiB, an essential gene for early stage of sporulation. The deduced product of sawE gene is a regulatory protein. sawE disruptant was blocked at aerial hyphae stage of Streptomyces ansochromogenes 7100, no sporulation septation, no formation of grey mature spore. Disruptants maintained white phenotype on prolonged incubation. The result indicated that sawE is essential for the morphological differentiation of S. ansochromogenes.