spawning stocks in the northern Yellow Sea between 1986 and 2010. The range and mean values of the four basic biological indicators (fork length, weight, net weight, and gonad weight) were significantly higher in 1986 than in 2010. In 1986, the age structure ranged from age 1⁺ to 7⁺ and was dominated by age 2⁺−3⁺ individuals. In 2010, the age range was reduced (1⁺−3⁺) and the dominant age was 2⁺. In 1986, the range in GSI was 3.43−21.87 (mean 11.63) and the mean GSI varied significantly among fish of different lengths. In 2010, the GSI ranged between 8.33 and 20.50 (mean 13.16) and there was little difference in mean GSI among different length groups. In both years, the gonads of female fish were primarily at stages and the GSI increased with increase in gonad maturity before spawning. The mean GSI increased between 1986 and 2010 for the same sized fish. The absolute fecundity ( grains (mean: 50.2502×10⁴±1.2615×10⁴) and the most common value was between 40×10⁴ and 70×10⁴ grains in 1986. In 2010, the range was 23.4520×10⁴−62.0805×10⁴ grains (mean: 40.7312×10⁴±2.1458×10⁴ grains) and the most common group was 30×10⁴−50×10⁴ grains. In 1986, the relative fecundity (r/L) was in the range of 269−2 519 grains/mm (mean: 1 467±33 grains/mm) with most fish being in the range 100−1 600 grains/mm). The relative fecundity was in the range 303−1 552 grains (mean: 1 041±21 grains/g) with most fish being in the range 900−1 300 grains/g). In 2010, the relative fecundity (r/L) was in the range of 798−1 864 grains/mm (mean: 1 279±36 grains/mm) with most fish being in the range 900−1 300 grains/mm). The relative fecundity was in the range 705−1 724 grains/g (mean: 1 170±31 grains/g) with most fish being in the range 1000–1 300 grains/g). Compared with 1986, the relative fecundity increased by 11.93% in 2010, while the absolute fecundity decreased by 18.45% within the same fork length range. These changes in the reproductive characteristics may be caused by simplification of the age structure, individual miniaturization, or growth acceleration in Scomber japonicus resources, we suggest the fishery administrative department should consider additional protective measures at the primary spawning ground and during the spawning period to limit the over harvest of spawning stocks in the East China Sea and Yellow Sea.