SigT is an ECF sigma factor in Streptomyces coelicolor. sigT and its putative anti-sigma factor gene rstA are located in one putative operon, and SigT could physically interact with RstA. Deletion of sigT or rstA caused accelerated morphological development and enhanced production of antibiotics, concomitant with over-expression of chpE, chpH, actII-orf4 and redD. Furthermore, SigT was undetectable after loss of rstA. These data suggested that SigT has a negative role on differentiation and that RstA negatively regulates the SigT activity through a putative antagonistic mechanism and at the post-transcriptional level.