Abstract: Objective To investigate the expression of 3-mercaptopyruvate sulfurtransferase (3MST) in medulla oblongata of neonatal rats and effects of intrauterine cigarette exposure on its expression. Methods Sprague Dawley pregnant rats were randomly divided into 2 groups, control group and cigarette smoke exposure group (n=8). 3MST mRNA and protein expression in medulla oblongata of neonatal rats were analysed by RT-PCR and Western blot, respectively, and the expression of 3MST in the neurons of respiratory-related nuclei in medulla oblongata of neonatal rats was investigated with immunohistochemical technique. Results The RT-PCR and Western blot analyses showed that 3MST mRNA and protein were expressed in the medulla oblogata of neonatal rats and intrauterine cigarette exposure promoted their expression (P<0.05). Immunohistochemical staining indicated that 3MST existed in the neurons of pre-B tzinger complex (pre-B tC), hypoglossal nucleus (12N), ambiguous nucleus (Amb), facial nucleus (FN) and nucleus tractus solitarius (NTS) in control group of the animals and the mean optical densities of 3MST-positive neurons in the pre-B tC, 12N, Amb and FN, but not NTS, were significantly increased in cigarette smoke exposure group (P<0.05). Conclusions 3MST exists in the neurons of medullary respiratory nuclei of neonatal rats and its expression can be up-regulated by intrauterine cigarette exposure, suggesting that the 3MST-H₂S pathway may be involved in protection of medullary respiratory centers against injury induced by intrauterine cigarette exposure.