The reproductive biology of chub mackerel, Scomber japonicus (Houttuyn, 1782) was studied for the first time in Larache coast from January to December 2005. Using gonadosomatic index (GSI) and gonad macroscopic observation, spawning season was estimated to be from December to March and in June and July with a peak in January. The mean total length at 50% of maturity was 22.88 ± 0.42 cm for males and 23.01 ± 0.31 cm for females. Regarding sex ratio, there was a significant difference in the number of males and females. Seventeen females were used for estimating fecundity. The mean fecundity (F) was 285,704 oocytes, ranging from 77,621 to 465,712. The mean relative fecundity was estimated to be 1567 eggs per gram body weight without ovary. The relationships between absolute fecundity [F x 1000] and total length [F = 651.95 Ln(TL) – 1841.1] and with somatic weight without ovary [F = 196.91 Ln(W) – 709.53] were of the logarithmic type.