Background: Oligohydramnios poses a challenge in obstetric management, particularly when it is diagnosed before term. Aim of the study was to determine whether oral maternal hydration alleviate isolated oligohydramnios in the third trimester of pregnancy. Research design: Quasi experimental design. Setting: the antenatal outpatient clinic and labor ward of labor and childhood hospital and El- Ahrar hospital in Zagazig, Egypt. Study Subjects: 104 pregnant women diagnosed as isolated oligohydramnios in the third trimester divided into: Intervention group (n=52) who were instructed to drink 2 liters of water over two hours, and this was repeated twice weekly throughout the third trimester till delivery. Control group (n=52) who follow daily routine hydration determined by thirst. Tools of data collection: present pregnancy record, labor record and newborn record. Results: At diagnosis, the mean AFI in the intervention and control group was 2.81± 1.28 & 2.75±1.33 respectively. In the intervention group, after two hours of maternal hydration and at labor, the mean AFI was highly statistically increased to 7.60± 1.56 & 6.63±1.39 respectively. Labor complications as preterm labor, induced labor and emergency CS complicated a highly statistically higher percentage of women in the control group than the intervention group 23.0%, 34.6% & 11.5% vs. 5.8%, 17.3% &0.0% respectively. A statistically higher percentage of women in the control group had abnormal CTG and doppler US compared to those in the intervention group (11.5% & 23.1 vs. 1.9% & 3.8% respectively). Conclusion: oral maternal hydration in isolated oligohydranmnios in the third trimester of pregnancy, resulted in highly significantly increased mean AFI after two hours and at labor. Moreover, maternal, fetal and neonatal complications were significantly decreased. Recommendation: Using maternal oral hydration for isolated third trimester oligohydramnios as a non invasive, cheap method for correction of oligohydramnios after complete maternal and fetal assessment. Key words: Oral hydration, isolated oligohydramnios, third trimester.