Small-scale sillago, Sillago parvisquamis (family Sillaginidae), is recognized as an endangered species in Japan. The only large local population of this species is found on the Nakatsu tidal flat in southern Suo-nada Sea (that is the Buzen-kai Sea) in the Seto Inland Sea, Japan. The population structure on the Nakatsu tidal flat was investigated in 2011-2013 to clarify recent population trends. It was found that 2011 constituted the dominant year class. The catch per unit effort (number of caught fish/3 hours/person) by rod-and-line fishing in June 2012 showed a high value of 7.4 (n=13) for the spawning season. This dominant year class was evident at all sampling stations in the Buzen-kai Sea. However, the same year class was not observed in the northern part of the Suo-nada Sea and adjacent waters. These results thus indicate that the dominance of the 2011 year class occurred only in the area of the Buzen-kai Sea.