Mesenteric fat weight (MFW) is a representative index used to reflect body lipid level in Ctenopharyngodon idella. However, the traditional measurements by artificial scrape and weighing are time-consuming, labor intensive and having high operating errors, especially when many samples are to be handled. To avoid such limitations, this study developed a rapid and sensitive method for the quantitation of mesenteric fat utilizing the lysochrome dye oil red O. The initial operation procedures included: fish anesthetization, sample collection of visceral mass, PIT-tag implantation, sample fixation, sample dehydration, oil red O staining. After the above steps, mesenteric fat could be specifically stained by oil red O dye, and all the samples were stained uniformly. After sample extraction and absorbance measurement of extraction liquid, the weight of oil red O extracted from the stained sample could be accurately obtained according to the standard curve of oil red O (y = 0.0276x + 0.0403, R² = 0.999 7). The oil red O weights were used as MFWs in this study, and had good consistency with the fat weights quantified by the conventional scraping method (r = 0.80). Furthermore, data analysis showed that the coefficient of variation for MFW (24.49%) was greater than that for body weight (8.93%) in the cultured population of C. idella (n = 200), indicating a significant potential for its genetic improvement. Correlation and cluster analysis showed that MFW was positively correlated with all the observed traits, of which visceral weight (VW) had the highest correlation coefficient of 0.60 (P ? 0.01), and was clustered into one group. The results were as expected that both MFW and VW belonged to viscera-related indexes. Multiple linear regression analysis showed that morphological indexes could explain only a small amount of variation for MFW (R² = 0.20), indicating that the regression prediction was unsatisfactory, and direct measurement remained an effective approach. This study provided an accurate quantitative method for genetic improvement of body lipid traits in C. idella.