Abstract: To obtain a comprehensive understanding of the fecundity characteristics of Argentine shortfin squids (Illex argentinus), we took the mature female individuals of I. argentinus from the southwestern Atlantic Ocean in 2021 as samples, and used a mixed effects model to analyze the relationship between the fecundity characteristics and the environmental factors in their habitat. The results show that the average effective fecundity of mature females was (67 061.72±24 147.00) oocytes, with a maximum egg diameter of 1.89 mm and a peak energy density of 26.21 kJ·g⁻¹. The effective fecundity demonstrated no significant variation across the sampling months, while notable disparities were observed in the oviduct egg size and energy density. The chlorophyll a concentration emerged as a key oceanic determinant influencing the effective fecundity, with the fecundity being comparatively substantial at concentration of 0.40~0.45 mg·m⁻³. Sea surface temperature, chlorophyll a concentration and sea surface height significantly influenced the oviduct egg size and energy density. The research suggests that environmental factors within the marine habitat have a significant influence on the effective fecundity, oviduct egg size and energy density of female I. argentinus. The allocation of reproductive energy by female squids is an adaptive process in response to environmental selection within their habitat.