The fisheries biology characters of Johnius belangerii,including size composition,relation of body length and weight,sex ratio,reproduction habits and diet,were analyzed based on the data collected from January 2009 to February 2010 off Ma’an Archipelago.Results showed that the body length range of J.belangerii was 30-264 mm,and the dominant body length groups were 80-100 mm and 130-180 mm.Juveniles and males showed a negatively allometric growth,while females showed a positively allometric growth.Sex ratio(females:males)was 1.68:1 and it varied with months and body length obviously except August and September and length groups 110-150 mm and 160-180 mm.The reproductive season was from June to September.The estimated ML₅₀ for females and males were 124.8 mm and 136.4 mm,respectively.The diet compositions changed along with month and body length.Juveniles mainly preyed on amphipoda and the adults mainly fed on fish and shrimps before reproduction and fed on amphipoda during reproductive period.The range of body length and length of dominant body length groups ofJ. belangerii,off Ma’an Archipelago were greater than other sea areas.Measures relating to reproductive stock and juveniles of J. belangerii protection should be taken in order to achieve continuous use of this species’ resources.