Background: Preterm premature rupture of membranes (PROM) , refers to rupture of membranes before the onset of labour in women with a pregnancy <37 weeks gestation. It complicates 1-3% of all pregnancies and is responsible for approximately 30% of preterm deliveries. Objective: This study aimed at examining the efficacy of a vaginal probiotic formula in combination with standard antibiotic prophylaxis on perinatal outcome in cases of PPROM before 34 weeks of gestation and comparing them with those treated only with antibiotics. Methods: This is a prospective randomized controlled study conducted at the department of obstetrics & gynecology and its out-patient clinic, El- Hussein University Hospital from august 1 st 2017 to august 1 st 2018 . Results: During the study period, 73 pregnant women diagnosed as PPROM were invited to participate. Two of them denied, while the remaining 71 women accepted participation in our study ( 2 women of the study group were excluded due to poor compliance to the study protocol and 1 of each group was also excluded due to delivery in the first 48 h after the study entry). In total 67 women were included in the study. In our study the cases diagnosed as PPROM were divided into 2 groups: Group 1 ( study group ) consisted of 33 cases and group 2 (control group) consisted of 34 cases . There was no statistical significant difference between the two groups as regard mean gestational age at admission , age, height, weight ,parity and gravidy (p value > 0.05). There was statistical significant difference between the two groups as regard history of PROM with higher cases in control group , gestational age at delivery (weeks) with higher percentage in study group and latency period with highly period in study group (p- value <0.05). Also, in the present study as regard neonatal outcome there were significant statistical differences between the two groups as regard 1 and 5-minute APGAR score after birth with highest low score in control group . Conclusion: This study demonstrated that the efficacy of a vaginal probiotic formula in combination with standard antibiotic prophylaxis on perinatal outcome in cases of PPROM before 34 weeks of gestation as compared to those treated only with antibiotics.