Introduction: The aim of this study is to determine some of the maternal risk factors that lead to preterm delivery. Recognizing these risk factors makes it possible to prevent preterm labors as the most frequent cause of neonatal morbidity and mortality. Materials and Methods: This is a descriptive-analytical research study. The data were collected from the recorded information in the files of mothers and preterm neonates that had been born in Bahman 22nd and Shahrivar 17th Hospitals in Mashhad during 2007-2009. The case group consists of 360 preterm deliveries (before week 37th of gestation). The control group consists of 360 term deliveries (after week 37th of gestation). In this study, some of the maternal risk factors leading to preterm labor were taken into consideration. The criteria selected were: maternity age, previous abortions, number of previous pregnancies, preeclampsia, the number and gender of fetuses, diabetes and bacterial vaginitis. Also, UTI, the premature rupture of membrane (PROM) was extracted from the registration records. Using SPSS, the two groups were compared and the data were analyzed with the method of chi- square test.Results: In this study, the prevalence rate of preterm labor was estimated as 6.1%. The findings suggest that maternal risk factors, such as diabetes, UTI, maternity age, the number of previous pregnancies and the gender of fetus did not cause any significant difference between the groups of the study, but we found significant p-value for the risk factors, such as bacterial vaginitis, PROM, preeclampsia, previous abortions, and the number of fetuses. Conclusion: We can reduce the incidence of preterm labor as a result of which the rate of morbidity and mortality of preterm neonates would decrease. This can be materialize through early diagnosis and treatment of maternal genitourinary infections, prevention of premature rupture (PROM) and preeclampsia as well as preventing repeated abortions and iatrogenic multiple gestation with induction of ovulation.