The fishes of the family Nemipteridae (order: Perciformes) popularly known as threadfin breams, are distributed in the tropical and subtropical seas. Nemipterus japonicas (Bloch, 1791), the Japanese threadfin bream, has wide spread distribution throughout the Indian Ocean and plays an important role in the commercial fisheries of west coast of India. Present study analyses the various aspects of Biology of N. japonicus along the coast of Ratnagiri, Maharashtra, such as length frequency. Length-weight relationship, food and feeding habits as well as reproductive development. The length-weight relationship equations analysed for Males were W = 4.1904 L 2.7671, females were W = 4.3385 L 2.6168, for indeterminate were W = 4.9880 L 2.9812 and for total were W = 4.4780 L 2.6285 indicating no significant difference between the sexes. The food and feeding habits revealed that N. japonicus is a voracious bottom feeding carnivore, feeding mainly on crustaceans. Studies on reproductive biology showed that N. japonicus is a fractional spawner and spawning season appears to be December to March.