Background: Preterm labour (PTL) is any delivery after 20 weeks and before the completion of 37 weeks' gestation. In preterm labour , the efficacy of tocolytic drugs has been proven to prolong pregnancy. A commonly used tocolytic drug is nifedipine which appears to be more effective than β2-adrenergic-receptor agonists and magnesium sulfate. The aim of the present study was to study the tocolytic action of nifedipine combined with sildenafil citrate and if the combination is superior to nifedipine alone in inhibiting threatened preterm labour. Methods: This interventional Study was conducted at Obstetrics and Gynecology Department, Zagazig University, from April 2019 to Febrile 2020. Included 96 pregnant women who suffered from threatened preterm labor. They were divided into two groups, group (A) included 48 cases who received Nifedipine only and group (B) included 48 cases who received Nifedipine with sildenafil. Results: our study showed that a statistically significant difference regarding maternal heart rate and mean blood pressure (mm Hge) before and after treatment in Nifedipine with sildenafil group group. But in Nifedipine only group, there was no statistically significant difference regarding maternal heart rate before and after treatment. There was statistically significant difference between the two studied groups in delivery 24,48 and 72 hours after admission with less early deliveries among the Nifedipine with sildenafil group. Regarding mode of delivery, there was no statistical significant deference between nifedipine and Nifedipine with sildenafil groups. Conclusions: Vaginal sildenafil citrate (SC) combined with nifedipine is an effective option for tocolytic therapy during threatened PTL.