Abstract: Fishery biology including catch stock composition, morphological properties, sex ratio, nidamental gland and gonad development of squid Illex Argentines were analyzed based on the 666 samples from the China’s fishing boat in the Southwest Atlantic Ocean during January to April 2012.The results showed that the mantle length ranged from 91mm to 351mm, showing a bimodal distribution, the average mantle length of females and males was 243.6mm and 214.5mm respectively, meaning that the size of female individuals was significantly bigger than that of males.The sex ratio of female to male was 1.26:1,and the females dominated in this stock.The sexual maturity was mainly in phase Ⅱ(57.9%), but the proportion of mature individuals above Ⅲ reached 42.1%. The sexual maturity and nidamental gland development of female were related to the individual size and further researches suggest that nidamental gland length-weight presented a power function, and nidamental gland index (NGI) of mature individuals was significantly greater than for the immature individuals. The male gonad gradually developed with its body size. According to body size and sexual maturity, the squid captured during the investigation was mainly South Patagonic Stock (SPS), mixed with a small amount of Summer-Spawning Stock(SSS).