The aim of this study was to investigate the therapeutic effect of inhaled Desmopressin (DDAVP) in pregnant women with idiopathic oligohydramnios. This randomized, double-blind clinical trial involved 44 pregnant women at 28–37 weeks of gestation with idiopathic oligohydramnios admitted in 2 academic hospitals in Mashhad, Iran, from 2018 to 2019. In the intervention group, 10µg DDAVP was nasally sprayed. The control group received intravenous maintenance fluid. The hematocrit, electrolytes, blood pressure and urine-specific gravity were evaluated at baseline and 3, 8, and 24 hours later. Amniotic fluid index (AFI) was measured using ultrasound at baseline, 24 and 48 hours later. There was no significant difference in the basic characteristics (age, body mass index, and gestational age) between the two groups. The pattern of changes of AFI (baseline, 24 and 48 hours later) increased in the intervention (4.16±0.86, 7.08±1.453 and 7.76±1.62, p<0.001) and control groups (4.23±0.70, 5.39±1.079 and 5.68±1.10, p<0.001). Serum sodium levels significantly declined in the intervention group (p<0.001) but not in the control group (p=0.07). There were no significant differences in potassium (p=0.89), hematocrit (p=0.23), systolic blood pressure (p=0.21) and diastolic blood pressure (p=0.97). However, urine-specific gravity had an increasing pattern in the intervention group (p<0.001) and a decreasing pattern in the control group (p<0.001). This study showed that Desmopressin inhalation could increase the AFI and urine specific gravity, enhancing oligohydramnios treatment in pregnant women, compared to serum administration.