Abstract: The present study was conducted to investigate the effects of dietary Eucommia ulmoides (EU) on growth performance, flesh quality, collagen genes COL1A1 and COL1A2 expression of grass carp (Ctenopharyngodon idella). A total of 120 grass carp with an initial body weight of (215.0±0.4) g were randomly allocated into 2 groups with 3 replicates per group and 20 fish per replicate. The fish were fed formula diet without (control) or with the supplementation of 2% Eucommia ulmoides (EU) for 8 weeks. The supplementation of 2% EU did not significantly affect the growth performance of grass carp when compared with the control (P>0.05), but increased the collagen content in muscle, skin and liver (P<0.05). Total essential amino acids (TEAA), total non-essential amino acids (TNEAA) and total amino acids (TAA) in muscle of grass carp fed EU diet were significantly higher than those of control group. Fish fed EU showed significantly lower flesh thawing loss and centrifugal loss (higher water holding capacity) (P<0.05), but muscle fiber density and muscle fiber diameter showed no difference between the two groups (P>0.05). Moreover, dietary EU significantly promoted the relative expression level ofCOL1A1 and COL1A2 mRNA in muscle, skin at the 4^th week, the 8^th week, and the expression in liver at the 8^th week (P<0.05). In conclusion, dietary EU could improve the flesh quality of large-size grass carp.