Objective: To compare the influence of ritodrine alone or in combination with nifedipine on maternal side effects and suppressing preterm labor. Materials and Methods: This retrospective study included 213 pregnancies with preterm labor (20–34 weeks) from May 2002 to April 2010 in Kyungpook National University Hospital in Daegu, Korea. Obstetric medical records were reviewed for both maternal characteristics and neonatal outcomes, including birth weight, Apgar score, admission to neonatal intensive care unit (NICU), ventilator support, and neonatal mortality. Maternal side effects such as tachycardia, pulmonary edema, and hyperglycemia were also reviewed. Results: Of 213 patients, 109 received ritodrine only and 104 were given ritodrine and nifedipine. There was no statistical difference between the two groups with regards to pregnancy outcomes and neonatal complications. Pregnancy prolongation over seven days was achieved more in the combination therapy group, with borderline statistical significance (59.6% vs. 72.1%, p = 0.055). Sixtynine cases experienced maternal side effects; four cases were categorized as serious and 65 cases were mild. Conclusion: In the treatment of preterm labor, the combination regimen of ritodrine and nifedipine can be more effective than ritodrine alone for prolonging gestation over seven days. Moreover, as the combination did not cause severe maternal side effects, it may be considered as a safe and effective method to prolong gestation in patients with preterm labor.