The species of Mugilogobius sp. (Japanese name: Izumi-haze) and M. chulae are both common species, sympatrically inhabiting the estuaries and tidal flats of Okinawajima Island. Some species of Mugilogobius has a urea cycle, and their processing ability is higher, especially in northern distributed species, such as M. abei and Mugilogobius sp. It is possible to differentiate their life history traits and habitats on the basis of urea processing ability. However, because little is known in detail of their life history and habitat, Mugilogobius sp. and M. chulae were investigated through monthly sampling conducted on the southern part of the Sashiki Tidal flat and Manko Wetland on Okinawa-jima Island, from January 2012 to January 2013. The spawning seasons of Mugilogobius sp. and M. chulae are from January to October and April to October, respectively, with peaks in the summer period (April to October), indicating that maturity in both species is closely related to changes in water temperature. A comparison with the spawning season of M. abei, a temperate region species, revealed the subtropical species to spawn over a longer period. Estimates of daily age from otolith analyses indicated the possibility of recruitment from other areas, since histological observations revealed mismatches of gonads and birthmonths between different spawning seasons, as estimated by back-calculations of daily age. The longevity of Mugilogobius species was about six months. The study also revealed the growth rate of Mugilogobius sp. to be similar to that of M. chulae. Mugilogobius chulae locally inhabited mangrove habitats, whereas Mugilogobius sp. showed wide habitat use and was less susceptible to decreasing habitat than the former. Accordingly, future conservation of M. chulae is dependent upon suitable mud habitat associated with mangroves.