Beak is one of the most important hard tissues of Cephalopoda which is usually used in fishery biology and biomass estimation.According to the 2 916 samples of short-fin squid Illex argentinus collected by Chinese squid jigging vessels from January to March in 2010 in Southwest Atlantic Ocean,the morphologic parameters were measured and the growth characteristics of beak were studied.The result of principal component analysis of twelve morphologic indices showed that upper hood length(UHL),upper crest length(UCL),upper wing length(UWL),lower hood length(LHL),lower crest length(LCL)and lower wing length(LWL)could be used to represent the length growth features of beak of each dome,and the ratios of HL to CL,RL to RL,RW to WL,LWL/CL and WL/CL could be used as indicators of entire growth for beak(upper beak and lower beak)growth,and the each dome growth,the entire beak growth impacted by sex,gonad maturity and individual size were analyzed by the analysis of variance(ANOVA)and least-significant difference(LSD).The results indicated that the UHL,UCL,UWL,LHL,LCL and LWL were closely related to sex,and for females or males,the UHL,UCL,UWL,LHL,LCL and LWL were closely related to gonad maturity and mantle length,however the ratios of HL/CL,RL/CL,RW/CL,LWL/CL,WL/CL were nearly constant without changing with sex,gonad maturity or different mantle length with the ratios of 78.04%,22.46%,17.28%,81.41% and 23.07% for upper beak and 50.69%,43.31%,1.13%,144.98% and 93.68% for lower beak respectively.This study suggested that there are significant effects of individual size on beak morphology of I.argentinus in the Southwestern Atlantic Ocean.