This study was conducted to investigate the effects of dietary Myriophylium elatinoides on growth performance, slaughter performance and immune organ indexes of Linwu ducks, and to find the suitable supplemental level of Myriophylium elatinoides in Linwu ducks diet. A total of 480 thirty-day-old Linwu ducks with similar body weight were randomly divided into three groups with four replicates per group and forty ducks per replicate. Ducks in group 1 (control group) fed a basal diet, and the others in the groups 2 and 3 were fed the experimental diets which contained 10% and 20% Myriophylium elatinoides, respectively. The experiment lasted for 28 days. Ducks were killed at 44 and 58 days of age to investigate body weight, carcass rate, half-eviscerated rate, eviscerated rate, breast muscle rate, leg muscle rate, subcutaneous fat rate and immune organ index. The results showed as follows:1) at 30 to 44 days of age and 45 to 58 days of age, the average daily gain, average daily feed intake and the ratio of feed to gain of group 3 were significantly higher than those of group 2 and control group (P<0.05), and there were no significant differences between group 2 and control group (P>0.05). 2) At 44 and 58 days of age, there were no significant differences in body weight, carcass rate, half-eviscerated rate, eviscerated rate, leg muscle rate and subcutaneous fat rate among all groups (P>0.05), and the breast muscle rate of groups 2 and 3 was significantly higher than that of control group (P<0.05). 3) At 44 days of age, there were no significant differences in thymus index, spleen index and bursa of Fabricius index among all groups (P>0.05). At 58 days of age, the bursa of Fabricius index of group 3 was significantly higher than that of control group (P<0.05), the spleen index of group 3 was significantly higher than that of control group and group 2 (P<0.05), but there was no significant difference in thymus index among all groups (P>0.05). In conclusion, dietary supplemented with 10% Myriophylium elatinoides has no obvious effect on growth performance, slaughter performance, and immune organ indexes of Linwu ducks.