Cobia with the advantages of seldom infected, low cost and tasty quality. Theproduction of cobia in Taiwan is increasing gradually. To establish the gradingstandard of cobia will help the founding of brand name and marketing of cobia. It willalso expand the markets for aquaculture farm. The average lipid contents of dorsalmeat of cobia are about 10.8 %, and 18.8% for ventral meat. The lipid contents varygreatly and difficult to discern by their appearance. So the difference of quality andquantity of lipid contents can be used as the standard of grading. In this study, theelectromagnetic scan (EM-scan) is applied to do the non-destructive analysis. Theestimate equation of water and lipid contents for cobia is obtained as the index of nondestructivequality assessment index.