Energy accumulation is a vital index to indicate the level of reserve for organisms, especially for semelparous cephalopod species due to their short life-span and fast growth. In this study, using the mathematical methods and technology of energy-density determination, the relationship between body weight and mantle length, as well as the energy accumulation of somatic tissues including mantle, arms, and fins, were investigated for the jumbo squid, off Peru. The squid specimens were randomly sampled from the catch of a Chinese jigger fleet during the fishing season from June to August 2014, in the high sea off Peru (10°26°S-17°17°S, 79°17°W-82°39°W), and a total of 173 specimens were collected (107 females, 66 males). The results showed that the averages of both mantle length (ML) and body weight (BW) in female were (262.12±38.33) mm and (541.69±251.69) g respectively; while in males, the values were (251.37±31.90) mm ML and (449.78±179.99) g BW respectively. The effect of sex on the exponent "b" of the BW-ML relationship was significant, suggesting that there was a significant difference in the body growth between female and male individuals. The maximum energy density was detected in the mantle tissue for both female and male individuals, with an average of (20.56±1.12) kJ/g and (20.67±0.76) kJ/g respectively; followed by the arm tissue, with an average of (20.09±1.25) kJ/g and (19.95±0.87) kJ/g respectively. For the fin tissue, the energy density was detected at the minimum value, with an average of (19.92±1.05) kJ/g and (19.63±0.96) kJ/g for female and male individuals respectively. For the same somatic tissue, there was no statistical difference in the energy density between females and males (>0.05). The energy accumulated in different somatic tissues, however, was significantly different (<0.05), and the mantle tissue was showed the highest energy accumulation. In females, the percentage of energy accumulation was about 63.14%, 25.23%, and 11.63% for the mantle, arms, and fins respectively. In males, the percentages were about 65.89%, 22.91%, and 11.20% for the mantle, arms and fins respectively. Meanwhile, the energy accumulated in the soma of the mantle, arms, and fins significantly increased with body growth for both female and male individuals (<0.05), and the energy significantly increased along with the distribution from lower to higher latitudes (<0.05). These findings indicate that the process of energy accumulation in the somatic tissues of off Peru is the procedure for feeding and body growth.