To investigate the mechanism underlying the regulatory effect of Met on broiler growth, the growth performance, organ development, serum profile, myogenic gene expression, and methylation of myostatin gene exon 1 region in response to dietary Met status were evaluated. A total of 192 one-day-old Arbor Acres broiler chicks were housed in 3-layer cages in a temperature-controlled room with continuous lighting. The temperature of the room was maintained at 32 to 34°C for the first 3 d and then reduced by 2 to 3°C per week to a final temperature of 20°C. Cages were randomly allocated to 2 dietary treatments with 6 replicate cages (8 males and 8 females/cage) per treatment. Control starter and finisher diets contained 0.50 and 0.43% Met, respectively. Corresponding values for a +Met treatment were 0.60 and 0.53% Met, respectively. The birds receiving the +Met diets had a greater (P < 0.05) G:F throughout the experiment. The +Met diets increased (P < 0.05) the relative weight of breast muscle and the concentrations of uric acid and triglyceride in serum at 42 d of age, whereas other serum measurements were not affected by treatments. Increased myogenic factor 5 (Myf5) and myocyte enhancer factor 2B (MEF2B) and decreased myostatin mRNA expression were observed in broilers fed the +Met diets (P < 0.05). However, methylation of myostatin gene exon 1 region was not different between groups. In conclusion, broilers fed the +Met diets increased breast muscle growth that was reflected in the expected expression of myostatin, Myf5, and MEF2B genes.