In the process of tuna for food, the unprocessed parts of the whole fish range from 30 to 35%, which are mostly used as animal feed stuff, and wasted. Thus, preliminary study on the recycling of the by-product was done to ultimately produce highly valuable products. The study was peformed on skin, skin flesh, tail flesh, dark flesh and abdominal flesh of the tuna. First, crude protein was the most abundant in the skin at 26.31%. About 21% of the crude protein were found in the other samples. Second, crude fat was greatly obtained in the skin at 15.58%. Interestingly, only 0.75% of crude fat was found in the dark flesh. Third, vitamin C and vitamin B group were highly measured in the abdominal flesh and the dark flesh, respectively. Importantly, docosahexaenoic acid (DHA, C22 : 6 $omega$ -3) and eicosapentaenoic acid (EPA, C22 : 6 $omega$ -3) which are highly unsaturated fatty acids, were abundant in the skin and skin flesh. To determine the effect of high temperature to the unprocessed parts, the samples were exposed to steam for 30 min. After this processing, 15-methylhexadecanoic acid (i-17 : 0) were in- creased in the skin flesh and the dark flesh. Furthermore, 3-hydroxytetradecanoic acid (3-OH 14 : 0), heptadecanoic acid (17 : 0), 2-hydroxyhexadecanoic acid (2-OH 16 : 0) and nonadecanoic acid (19 : 0) hat were not found before with steam were detected. The DHA and EPA in the dark flesh and the DHA in the skin were stable, respectively, even after the treatment.