A total of 4 strains (DR2-4, DW2-1, DS2-1 and DS3-1) of undescribed ascomycetous yeast, isolated from Nam Nao forest soil, were identified as a novel species in the genus Millerozyma. The D1/D2 sequences of the strains differed from the closely related species Millerozyma acaciae and Pichia koratensis by 1.2% (7 nucleotide substitutions) and 1.4% (8 nucleotide substitutions). Phenotypically, all the novel strains were identical, but differed from M. acaciae and P. koratensis by a variety of phenotypic characteristics. Based on phenotypic and phylogenetic data, these four yeast strains were assigned to a single novel species in the genus Millerozyma and the name Millerozyma phetchabunensis sp. nov. is proposed. In addition, we also propose the transfer of P. koratensis, which was placed in the Millerozyma clade based on the analysis of the D1/D2 and ITS sequences, to the genus Millerozyma as M. koratensis comb. nov.