Abstract: The experiment investigated the effects of zinc sulfate heptahydrate supplementation in feed on the growth performance, muscle quality traits, and fat metabolism in grass carp (Ctenopharyngodon idella). Three isonitrogenous and isolipidemic feeds were formulated using zinc sulfate heptahydrate as the zinc source: the control diet (Con) and the experimental diet supplemented with 50 and 100 mg/kg zinc contents (Zn50 group and Zn100 group, respectively). A total of 135 grass carp with an initial body weight of (41.70±0.20) g were randomly assigned to three dietary treatment groups and fed with the experimental feed respectively. Each treatment group consisted of three replicates, and the feeding trial lasted for 50 days in an indoor recirculating water system. The results showed that there were no significant differences in growth performance between the Zn50 and Zn100 groups compared to the control group (P>0.05). However, compared with the control group, the muscle zinc content, hydroxyproline, and collagen levels of grass carp muscle quality traits in Zn50 and Zn100 groups increased, and the muscle crude fat content decreased significantly (P<0.05). The Zn100 group showed a significant increase in muscle crude protein content and muscle hardness (P<0.05). Additionally, regarding muscle fiber composition, the Zn50 group significantly reduced the proportion of muscle fibers with diameters>50 μm (P<0.05). In contrast, the Zn100 group significantly increased the proportion of muscle fibers with diameters <20 μm and 20-50 μm, significantly reduced the proportion of fibers >50 μm, and significantly increased muscle fiber density (P<0.05). Moreover, in terms of fat metabolism, zinc supplementation significantly downregulated the expression of fat synthesis-related genes (srebp-1, acc, fad, and fas) while upregulating the expression of fat decomposition-related genes (cpt1a and cpt1b) (P<0.05). Furthermore, the transcriptional levels of myogenic regulatory factors (myod, myog, and mrf5) were significantly upregulated in the Zn100 group (P<0.05), while no significant differences were observed in the expression of mrf4 and myosin heavy chain between the Zn50 and Zn100 groups compared to the control group (P>0.05). In conclusion, the dietary supplementation of zinc sulfate heptahydrate can improve muscle quality traits in grass carp, including muscle hardness, by increasing muscle collagen content and fiber density while reducing muscle crude fat content.