This study was to determine the effectiveness of guanidine aceticacid (GAA) with or without methionine in comparison with creatine (CREA) at enhancing duck’s performance, restoring tissue CREA and improving meat quality. Mulard ducklings (n=250) were fed on control diet or control diet plus CREA; GAA; GAA with 0.2% methionine (Met) (GAAMet0.2) or GAA with 0.4%Met (GAAMet0.4). Dietary supplementation of CREA or GAA significantly increased (P≤0.05) overall body gain and improved feed conversion ratio. The eating and drinking frequencies were the highest in GAA and CREA and the lowest in GAAMet0.4 and GAAMet0.2, ducks reared in GAAMet0.4 and GAAMet0.2 diets were more active, as expressed by greater frequencies of walking, body shaking and preening behavior and lower frequencies of lying, huddling and standing. There were highly significant differences observed in standing and huddling behavior between groups. Dietary GAA especially with 0.4% of Met significantly increased (P≤0.05) carcass and breast yield. The meat pH values were higher (P≤0.05) with dietary CREA or GAA supplemented with Met. Providing of a dietary GAA especially with Met led to higher levels of plasma CREA. Results suggested that dietary CREA or GAA with Met had the positive effect on duck’s performance and behavior. Also, dietary GAA enhanced tissues CREA loading than dietary CREA and long term of GAA supplementation in ducks may induce a methyl group deficiency that was resolved with Met addition.