Type-II polyketide synthases (PKS) are composed of two β-ketoacyl synthase subunits (KSα and KSβ) and one acyl carrier protein, which are involved in the biosynthesis of polyketide molecules. In this study, we investigated the diversity of type-II pks genes in 83 Streptomyces strains listed in the catalogue of the NITE Biological Resource Center (NBRC, http://www.nbrc.nite.go.jp/e/index.html) by determining partial sequences of the KSα genes. As expected, KSα genes were detected in 9 strains that have been reported to produce aromatic-polyketides. More interestingly, novel KSα genes were detected in 55 out of 74 Streptomyces strains so far unknown to produce aromatic antibiotics. The antibiotic-type KSα genes exhibited a high degree of divergence, the pairwise nucleotide similarities ranged from 67 to 95%. The existence of novel cryptic KSα genes in the Streptomyces strains suggest their potential to synthesize new aromatic polyketides.