Brasiliomyces Vieas is a powdery mildew genus characterized by chasmothecia without appendages and consisting of a single layer of peridium cells. This report is a part of a comprehensive study of Brasiliomyces with the final aim of clarifying the phylogenetic affinities of the Brasiliomyces within the Erysiphaceae. In this study, two new species of Brasiliomyces found on Castanopsis and Lithocarpus in northern Thailand are proposed. The first species forms scattered colonies of white, mainly epiphyllous and amphigenous, appendages of chasmothecia poorly developed, appressoria coral-like, chasmothecia contains 2-4 asci, and ascospores 4-6 per ascus, hyaline and ellipsoid-ovoid. The second species differs from the former species by having hypophyllous colonies on host leaves, chasmothecia comprise only 2 asci, and ascospore number in asci mostly 6-8. Phylogenetic analysis based on ITS rDNA region also showed that the new species form each distinct clade. Key words: phytopathogenic fungi, powdery mildew, taxonomy, tropics