A total of 441 Chilean jack mackerel (Trachurus murphyi) were collected by two large scale trawlers named “KAIXIN” from September to October 2010 and “KAIFU” in August 2011 in the southeast Pacific Ocean. In this paper, the histology of ovary was studied. The main results are: (1) The development of oocytes of Chilean jack mackerel was composed of five phases. In the phase 2 of oocyte development, there appeared a transparent layer in the outboard of nuclear membrane. A lot of yolk granules and lipoid vesicles formed in the cytoplasm during the phase 3 of oocyte development. Some of the nuclear membranes began to dissolve when the phase 4 came and we could find micropyle near the animal polar. The mature oocytes were apart from follicle membrane in the phase 5 of oocyte development. (2) The size distribution of eggs showed there were varied oocytes in the ovary of stage Ⅳ and there were two obvious pinnacles in the figure. (3) The spawning pattern of jack mackerel is multiple spawning that we could find more than one phase of oocytes in the same ovary at the same time. (4) The gonads were developing at a high speed from late August to early October.