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A great number of drugs have been used to inhibit preterm labor but none has been completely effective. This study has compared. The efficacy of Indomethacin and Mg-Sulfate for delaying delivery in preterm labor. In this randomized controlled trial study 120 pregnant women with intact membrane and preterm labor, cervical dilatation at least 2 cm were studied and if they had premature rupture of membranes, gestational age less than 24 or more than 32 weeks, complete cervical dilatation, severe hemorrhage, chorioamnionitis and triple or higher order gestation excluded from study. Subjects are randomly managed with Indomethacin 25 mg every 6 hours for 4 doses or Mg-Sulfate initially 4 gr/IV followed by 2 gr/h IU infusion until uterine activity diminished or decrease. The success of management was considered as either reduce or stopping the uterine contractions, and no increase in cervical dilatation or effacement. Statistical analysis were performed with Chi-square and T-test. The 2 groups understudy had the same inducer maternal matched maternal age, gestational age, parity, dilatation and effacement at initiation of study, frequency of uterine contractions. Delivery was delayed 24 hr in 66.6% and 48 hr in 58.3% by Mg-Sulfate, also delayed 24 hr in 40% and 48hr in 35% by Indomethacin (P<0.0001). No complications were reported in each group. Mg-Sulfate is more effective than Indomethacin in delaying preterm labor.