Guanidinoacetic acid (GAA) is a natural precursor for creatine, which is involved in physiological energy generation. Six hundred and ninety-nine weaned pigs (6-30 kg) were fed a basal diet (Diet 1-4, corresponding to four phases) without (CTRL) and with 0.12% GAA supplementation. Pigs in the CTRL group displayed higher (P < 0.05) average daily gain and lower feed conversion ratio, and body weight, during the periods of Diet 1 and 2, compared with GAA pigs. In the period of Diet 3 CTRL pigs tended (P < 0.10) to be heavier than GAA pigs, whereas in the period of Diet 4 GAA pigs tended (P < 0.10) to grow faster than CTRL pigs. Over the entire experimental period CTRL compared with GAA pigs displayed improved feed efficiency (P < 0.05) and tended (P < 0.10) to grow faster. In conclusion, GAA did show minor potential to increase average daily gain in the last part of the weaning phase.