The mudskipper, <i>Periophthalmus barbarus</i> is reported to be a good delicacy for human consumption as well as for use in traditional medicinal preparations where aphrodisiac properties are attributed to its flesh. They are investigated for their biological and eco-toxicological studies, to determine its potential use as a bio-indicator in environmental assessments of coastal waters, tropical or subtropical soft bottom intertidal systems, and despite this; there is lacuna of scientific report on its biology and ecology. This research was undertaken to provide information on the aspects of the biology of the species, with reference to sexual dimorphism, sex ratio, size composition, gonad morphology and morphogenesis, length weight relationship and condition index. Monthly samples were collected at Jaja creek, Niger Delta, Nigeria and preserved in 10% formalin for further analysis. Length and weight of each specimen were measured and weighed to the nearest 0.1 cm and 0.001 g respectively; the specimens were later dissected to examine the gonads. Ovaries and testes from each specimen were measured and weighed to the nearest 0.001 g and 0.1 cm respectively. Paired comparison by the observation of the genital papilla on the postero-ventral surface of the abdominal region was used to determine sexual dimorphism in weight in similarly-sized females and males. The proportion of the two sexes relative to one another was used to calculate the sex ratio. Each specimen was measured using a fish measuring board to the nearest centimeter and weighed using a meter balance to nearest gram and recorded to obtain size composition. The length-weight (L-W) relationship was computed using empirical allometric equation. Findings reveal that the presence of spermatocytes and oocytes at different stages of development was an indication that this species belongs to the fish with prolonged and fractional spawning season and therefore, may spawn more than once during the spawning season. The mean condition index of 1.06 proved that the fish fed well and was in a good condition. The pattern of length-weight relationship revealed positive allometric growth.