Abstract: Argentinean shortfin squid, Illex argentinus is well documented for short life span, fast growth, and semelparity. Hence, the growth and the body condition changes can effectively reflect its life history strategy with respect to energy accumulation and reproductive investment, which subsequently influence the final reproductive efforts and recruitment biomass. This study randomly collected I. argentinus from the feeding ground in the southwest Atlantic during 2012 and 2014 to analyze the body weight—mantle length relationship and the body condition changes by using methodologies of residual index analysis and generalized linear mixed-effects models. The results showed that the overall sex ratio of female to male was 1.25﹕1. The mantle lengths of female and male in 2014 were (271.7±28.3) mm and (244.7±17.3) mm, respectively. There were no significant differences in the mantle length between sampling years of 2012 and 2013. The specimens were (207.9±31.0) mm for females and (201.1±28.9) mm for males in 2012, and there were (213.6±18.0) mm for females and (203.5±19.0) mm for males in 2013. The body weight significantly associated with mantle length for female and male I. argentinus based on power function algorithm, and the coefficient b was different from the isometric growth coefficient b=3 for the specimens from each sampling year. There were significant differences in the body condition among sampling years for both female and male. The body condition was significant difference among each month for each sex except for the female in 2012. Moreover, the interactions between mantle length and month imposed a consistent influence on the body condition, that is, the larger body size with decreased body condition. Cumulatively, these evidence indicate that the growth of I. argentinus is allometric, the body condition is significant different between sampling years and sampling months, and the body condition is negatively related to the mantle length.