The 3-amino-5-hydroxybenzoic acid (AHBA) synthase is one of the essential and unique enzymes for AHBA biosynthesis. The possibility of screening for ansamycin or AHBA-related antibiotic-producing strains from Actinomycetes by targeting an AHBA synthase gene was explored. A pair of degenerated primers designed according to the conserved regions of five known AHBA synthases was used to detect AHBA synthase genes within the genomic DNA of Actinomycetes. PCR screening resulted in obtaining 33 AHBA synthase gene-positive strains from 2000 newly isolated Actinomycetes. Phylogenetic analysis of these gene fragments along with those involved in the biosynthesis of structurally determined ansamycins showed that the genes with close phylogenetic relationships might be involved in the biosynthesis of compounds with the same/similar structures. Four strains have been proved to be actual geldanamycin or rifamycin producers by chemical characterization of their fermentation products. The results confirmed the feasibility of using the AHBA synthase gene as a probe in polymerase chain reaction (PCR) screening of ansamycin or AHBA-related antibiotic-producing strains. The PCR screening of AHBA synthase gene represents a direct and sensitive molecular method for rapid detection of AHBA-related antibiotic-producing strains.