Round secad (Decapterus maruadsi), a widely distributal fish.is one of the main targets for purse seine fishing in China. This study is based onobservation of scales and otoliths of 644 fishes collected from commercial catches offZhejiang coast from January of 1981 to March of 1983. The results are summarized asfollows: 1. The scales and otoliths are reliable in age determination of this species. Newrings are formed once a year, and they usually appear in May and June. 2. The body length and the scale length prescnt a linear relation: L=1.259R-2 .691.The correlation equation of the body length and weight is W=1.652×10~(-5)L~(2.947). 3. The growth rate of the fish is uneven within a year. The growth is rapidfrom May to Oct. and is slow from Nov. to April. 4. The general law of growth between years may be expressed by von Dertalanf-fy growth equation. The changing feature in the growth process is charanacterized bythe body length and weight tending towards the asymptotic value with the increase oftime. The growth rew and acceleration tend to the zero gradually, The length seemedto be more rapid tending to the terminal than the weight.