Otoliths were examined from 581 fish specimens that were collected from August 1997 to April 1998 in the mouth of the Hei River, and 300 fish specimens were collected from April to June in 1998 in spawning site of the Hei River. Results of those examinations revealed the age composition of anadromous wakasagi, Hypomesus nipponensis. The opaque zone and translucent zone are formed sequentially: the first translucent zone (T1) is formed in August-November and the first opaque zone (O1) is formed in October-April; the second translucent zone (T2) is formed in May - September and the second opaque zone (O2) is formed in August - April. This study found that a 0+ year-old fish forms a first opaque zone (O1), whereas a 1+ year-old fish forms a second opaque zone (O2) in their respective otoliths. Based on those findings, 609 fish specimens were collected at the spawning site of the Hei River from April to June in 2001. They were examined to determine their age composition. Both 0+ and 1+ year-old fish were found in the spawning site of the river.