This paper studies on the individual fecundity of the mackerel,Scomberomorus niphonius in the Yellow Sea and Bohai Sea, based on 114 ovaries collected from late May and early June in 1992 and 1993 , that 27 ovaries of them were observed through histologic method. The results are showed as follows: 1. The ova diameter can be graded into 5 size classes: the yolkless oocyte with a diameter of 0.007-0. 490 mm in the second phase, the small oocyte of 0. 364-0. 714 mm in the third phase, the middle oocyte of 0. 728-0.966 mm in the early fourth phase, the large oocyte of 0. 98o-1. 540 mm in the mid and late fourth phase, and the transparent oocyte of 1. 375-2. 030 mm in the fifth phase.2. According to the frequency distribution of ova diameter in the ovary, the ripe ova more than 1. 3 mm are released 2 or 3 batches during spawning period.The oocytes more than 0. 4 mm in the third phase may be matured succesively in late spawning season.3. The individual absolute fecundity is ranged from 45 to 5257 thousand. The relative fecundity is ranged from 62 to 770 eggs/g per unit body weight or from 66 to 957 eggs/g per unit net body weight. Both absolute and relative fecundities increase with the age, body length and body weight of the fish.