Preterm labor is one of the major causes of neonatal mortality and morbidity. Despite significant improvement in care for premature neonates, the most suitable and inexpensive treatment is prevention of preterm labor by inhibiting uterine contractions. The aim of this research is to obtain scientific evidence for the relaxant effect of ketotifen on the rat uterus and to provide the preclinical information that may indicate the clinical usefulness of ketotifen in preterm labor. Our studies have shown that ketotifen is a potent uterine muscle relaxant for contractions induced by oxytocin. Compared to controls and samples exposed to diazoxide (a vasodilator) and terbutaline (a β₂-adrenergic agonist), we conclude that ketotifen is more effective than diazoxide and similar to terbutaline.