In 1982, an anamorphic fungus in the genus Monilia was first isolated as the causal agent of brown rot disease of Japanese apricot or mume (Prunus mume) in Oita Prefecture, Kyushu, Japan. Inoculation of flowers, shoots, and fruit of P. mume with the fungus reproduced brown rot disease symptoms similar to those found in nature. The fungus somewhat resembled the colony appearance of Monilinia (anamorph Monilia) laxa, the apricot brown rot fungus, on PSA plates, but it differed from the latter and the other two brown rot fungi, M. fructigena and M. fructicola, in terms of growth rate, temperature optima for mycelial growth and sporulation, morphology and germination pattern of conidia, nuclear number in the conidium, and nucleotide sequences in the ITS region of ribosomal DNA. It is newly described as Monilia mumecola Y. Harada, Y. Sasaki & T. Sano. A key to anamorphic states of four brown rot fungi of fruit trees is provided.