The energy sourcing for reproduction in short-life cephalopod species is vitally important for the successful development of reproductive organs, in which the energy acquisition and allocation to gamete production would be greatly in relation to their reproductive strategies. Therefore, by using the technology of energy density determination combined with residuals analysis, we investigated the energy accumulation and allocation in both soma and reproductive organs of Argentinean short-fin squid Illex argentinus, an important cephalopod species, to provide further evidence whether the reproductive investment comes from food intake or diverts from the somatic growth. The tissue energy density was determined for the arms, mantle, ovary, nidamental gland and oviducal complex, where it had an average value of (22.75±0.60), (23.42±0.68), (25.15±2.08), (21.49±1.46) and (25.12±3.02) kJ/g, separately. There was no statistically significant difference in the energy density between different sexual maturity stages for the tissue of arms, mantle, and nidamental glands separately. However, the energy density was significantly different between sexual maturity stages for ovary and oviducal complex separately. Both arms and mantle attained their maximum tissue energy at maturity stage III. In the reproductive system, ovary attained its maximum tissue energy at maturity stage V, whereas both the tissue energy of nidamental gland and oviducal complex were gently increasing with maturity and attained their maximum value at maturity stage VI. Specifically, the tissue energy of oviducal complex had a burst increase after maturity stage IV onwards. At the same maturity stage, the somatic tissue energy, calculated as the sum of mantle and arms tissue energy, was always in the larger proportion, while the tissue energy of reproductive organs, calculated as the sum of tissue energy of ovary, nidamental gland and oviducal compex, accounted for a smaller percentage. However, the proportion occupied by somatic tissue energy was decreasing gradually, while that by reproductive organ was increasing with maturation. The soma energy was partly remobilized for reproduction from maturity stages III to V, but this process of remobilization did not impact the integrity of somatic tissues. These findings confirm that the reproductive investment in I. argentinus is mainly from food intake, but along with some energy remobilization from soma during the sexual maturation.