Some behaviors such as roaming and fighting observed in weaned pigs have been considered to be unhelpful to growth performance. Melatonin (MEL) secreted from the pineal gland has a sedative effect on human behavior. In this study, MEL was supplemented in the weaned pig diets to determine the effect of MEL on growth performance and behaviors, and correlation between them. Two hundred twenty-five 21-d-old pigs were allotted into 4 treatments (9 or 10 pigs per pen) with 6 replications and fed diets containing MEL at doses of 0, 25, 50 and 100 mg/kg of diet (M0, M25, M50 and M100) for 35 d. By using closed-circuit television cameras, the behavior of pigs was recorded to score resting (RT), roaming (RM), feeding (FD) and fighting (FT) states for 24 h on d 3, 10, 17, 24 and 31. The BW and feed intake were measured every week to calculate ADG and feed efficiency (FE). The data were analyzed by ANOVA, followed by the Duncan’s new multiple range test. Correlations between growth performance and the behaviors were analyzed with reference to the Pearson correlation coefficients. The BW was higher in M25 group (not different from M0) than M50 and M100 groups on d 28 (P < 0.05) but there was no difference at the end of experiment. The ADG was higher in M25 group than the other groups during d 21–28 (P < 0.05). There were no differences in ADFI and FE throughout the experiment. The RT was lower and RM was higher in M50 group (not different from M0) than M25 and M100 groups on d 10 (P < 0.05) but there were no differences on the other days. The MEL did not alter FD and FT throughout the experiment. Correlations between growth performance and behavior were found in M0 group but not in MEL-treated groups (M25, M50 and M100) during d 7–14. Therefore, it is concluded that MEL at dose of 25 mg/kg of diet may affect BW in weaned pigs on d 28 according to the improved ADG during d 21–28 but MEL does not affect ADFI and FE. This study also suggests that MEL affects RT and RM within 14 d. However, the behaviors affected by MEL are not correlated with growth performance.