Background: Globally, it has proven that preterm birth is associated with perinatal mortality to the extent of >75%, and >50% of perinatal and long term morbidity. Oral progesterone are easy to take but are less effective because of first pass hepatic metabolism leading to variable plasma levels while intramuscular progesterone carries the risk of swelling and bruising at injection site. The aim was to find out frequency of preterm birth in patients treated with oral versus intramuscular progesterone.Methods: Randomized controlled trial conducted in the department of obstetrics and gynecology, Sir Ganga Ram hospital Lahore, Pakistan conducted from 5 October 2017 to 4 April 2018. This study involved 530 pregnant women with history of at least 1 previous preterm delivery presenting in antenatal clinic between 16-20 weeks of gestation. Group I received oral progesterone 10 mg tablet duphaston BD from 20 weeks till 37 weeks. Group II received intramuscular progesterone injection proluton depot 250 mg IM weekly from 16-20 weeks till 37 weeks.Results: The mean age of the patients was 27.52±4.57 years while the mean gestational age was 17.39±1.38 weeks. 47.5% of the patients were para 2 followed by para 3 (32.3%) and para 1 (20.2%). The mean gestational age at delivery was significantly higher among intramuscular group (36.14±2.23 versus 35.07±2.97 weeks; p=0.000). The frequency of preterm delivery was significantly lower in intramuscular group (24.9% versus 39.6%; p=0.000) as compared to oral group.Conclusions: Frequency of preterm delivery was significantly lower in patients treated with intramuscular progesterone (24.9% versus 39.6%; p=0.000) as compared to oral progesterone.