An experiment was conducted to determine the response of broiler chickens to guanidinoacetic acid (GAA) added to diets with different energy levels during fattening to 35 days of age. Ross 308 male chicks were allotted to 10 treatments, each consisting of six replicates of 140 birds/pen. Five maize-soyabean meal isonitrogenous diets with decreasing AMEn levels (100, 99, 98, 97 and 96% of requirement) with or without supplements of 0.6 g/kg CreAMINO® containing a minimum of 96% GAA were formulated. The criteria of response were feed intake, body weight gains, feed conversion ratio and carcass, breast meat, leg meat and abdominal fat yields. Supplementation of broiler diets with 0.06% GAA resulted in a significant (P < 0.05) decrease in voluntary feed intake. With decreasing AMEn level, voluntary feed intake and consequently protein and amino acid intakes increased which was manifested by improved growth performance (P < 0.01). GAA supplements significantly (P < 0.001) improved feed conversion ratio and efficiency of AMEn utilization and significantly (P < 0.01) increased breast meat yield. With decreasing AMEn level, the effects of GAA supplementation tended to diminish.