Abstract: Illex argentinus is one of the most important ommastrephid squids, due to its annual landing volume, and its key role as transient ‘biological pumps’ in southwest Atlantic ecosystem. In order to understand the fecundity characteristics of male ommastrephids, specimens of male I. argentinus, collected from December 2012 to March 2013, were used to analyze the fecundity and its relationship to reproductive development with biological statistics analysis. The results showed that the minimum biological size was 207.29 mm for mantle length (ML) and 162.55 g for body weight (BW). The effective fecundity (EF), defined as the sum of normal spermatophores in spermatophoric complex and spermatophoric sac, was in an average of (374±280.33) spermatophores. The mean value of relative effective fecundity by mantle length was (179.18±117.66) spermatophores per millimeter. The length of spermatophores (SL) varied from 6.34 to 33.14 mm, and its mean value was (21.57±4.17) mm, which was (10.22±1.82)% of mantle length. Both EF and SL significantly increased with the onset of sexual maturation (P<0.05). EF attained the maximum value at functionally maturity stage (Ⅵ), with a mean value of (811±181.34) spermatophores. SL increased up to the mating stage (Ⅶ), whereby it attained a mean value of (23.89±3.87) mm. Meanwhile, both EF and SL showed significantly linear relation with mantle length (EF=–581.92+4.56ML, R²=0.17, P<0.05;SL=5.77+0.075ML, R²=0.23, P<0.05) and body weight (EF=16.55+1.77BW, R²=0.37, P<0.05;SL=17.96+0.017BW, R²=0.17, P<0.05), indicating that individual with bigger size has larger EF and longer SL. Furthermore, the compare datasets of fitted model analysis revealed that there was no significant difference between the linear relationship of EF-ML and that of EF-BW (P>0.05). Based on multiple regression analysis, however, the influence on EF from body weight was more significant than that from mantle length (P<0.05). The compare datasets of fitted model analysis for SL showed that there was significant difference between the linear relationship of SL-ML and that of SL-BW (P<0.001), although the multiple regression analysis suggested a comparative influence on SL from both mantle length and body weight (P<0.001). These findings indicated that the EF of maleI. argentinus was a strategy of adaptability to its short lifespan by producing and accumulating spermatophores along with reproductive development and body growth, and the length of spermatophores will also increase with time.