Oculocutaneous albinism (OCA) is a complex genetic disease with great clinical heterogeneity. Four different types of OCA have been reported to date (OCA1, OCA2, OCA3, and OCA4). MATP was recently reported in a single Turkish OCA patient as the fourth pathological gene, but no other patients with OCA4 have been reported. Here, we report the mutational profile of OCA4, determined by genetic analysis of the MATP gene in a large Japanese population with OCA. Of 75 unrelated patients that were screened, 18 individuals (24%) were identified as having OCA4; they harbored seven novel mutations, including four missense mutations (P58S, D157N, G188V, and V507L) and three frameshift mutations (S90CGGCCA→GC, V144insAAGT, and V469delG), showing that MATP is the most frequent locus for tyrosinase-positive OCA in Japanese patients. We discuss the functional melanogenic activity of each mutant allele, judging from the relationship between the phenotypes and genotypes of the patients. This is the first report on a large group of patients with OCA4.