Abstract: Objective To study the serum concentrations of melatonin(MT), 5-hydroxytryptamine(5-HT), prolactin(PRL) and nitric oxide(NO) in cases with infant spasms(IS), and explore their correlations with occurrence of IS. Methods Thirty-nine infants with IS were recruited from our department from March to September in 2017, and another 42 infants with respiratory or urinary tract infections who had no history of neurological diseases, especially epilepsy, were recruited as controls. The serum level of MT, 5-HT, PRL and NO were measured by the enzyme linked immunosorbent assay(ELISA). And their expression levels in IS group before and after ACTH treatment were compared. Results The serum concentrations of MT and 5-HT in the IS group were significantly lower than those in the control group (7.1±1.9) pg/ml vs(11.2±1.8) pg/ml;(1 183.3±258.9) mIU/L vs(1 488.2±241.6) mIU/L;P< 0.05, respectively, but the serum concentrations of PRL and NO were significantly higher than those in the control group (523.1±109.4) mIU/L vs(358.0±80.7) mIU/L;(101.3±22.1)μmol/L vs(72.9±20.8)μmol/L; P< 0.05, respectively. The serum concentrations of MT (9.2±1.9) pg/ml and 5-HT (1 366.0±236.9) pg/ml in the IS group elevated significantly after ACTH treatment(P< 0.05, respectively). However, the serum concentrations of PRL (408.2±93.4) mIU/L obviously decreased after ACTH treatment(P< 0.01). There was no significant change in the serum concentration of NO(96.3±21.9)μmol/L after ACTH treatment(P=0.261). Conclusion Compared with the control group, the serum levels of MT and 5-HT are significantly lower in the IS group, while PRL and NO levels elevate significantly. After ACTH treatment, the serum levels of MT and 5-HT increase, while PRL level decrease and NO level doesn't change. Therefore, it is speculated that the abnormal levels of melatonin and its related hormones may play important roles in the pathogenesis of infantile spasms.