The purpose of this study was to use a rapid nondestructive technique to analyze the proximate composition of cultured eels. The processing conditions could be adjusted in accordance with the calculated composition of the eels. We were able to forecast the composition of live eels before processing. The eels can thus be harvested only when they reach the optimal condition for processing.Two species of market-size eels, Japanese eel (Anguilla japonica) and European eel (A. anguilla) from an intensively cultured system were randomly sampled for this study. The total body electrical conductivity (TOBEC) values of 50 individuals for each species were measured using electromagnetic scanning (EM-scan). TOBEC values were regressed against moisture, ash, crude protein, crude lipids, and lean body mass (LBM), and all of which showed significant linear correlations.The predicted equation and experimental measurements were tested using paired t-test. Results showed that length and weight values within the ranges used in this experiment (Japanese eel 151 ~ 483 g, 45 ~ 69 cm; European eel 143 ~ 438 g, 41 ~ 61 cm) could feasibly be used for predicting the proximate composition of cultured eels. The prediction for moisture, crude protein, and LBM was more accurate than for crude lipid and ash contents.