The influence of intramuscular (IM) administration of dexamethasone on labor duration in primigravidas was assessed. An observational prospective case control design was used. Data collected from two Maternity and Child Healthcare Centers, over three months using a pre designed assessment tool conducted by the researchers.. The study sample was selected by purposive random sample technique. The sample consisted of 172 primigravidas women who had favorable cervix with a bishop score of 7 or greater, pregnancy duration of at least 37 weeks, a first trimester ultrasound, and a vertex presentation of a singleton fetus. Primigravidas with maternal systemic diseases, pre mature rupture of membranes (PROM), and vaginal bleeding were excluded. The sample was divided into two equal groups. The experimental group (86 primigravidas, 43 from each center) received an intramuscular injection of 8 mg (2ml) of dexamethasone, and the control group (86 primigravidas, 43 from each center) received a placebo of IM injection of 2 ml of saline. Data was analyzed using SPSS Version 17. Data results revealed that women received (IM) injection of dexamethasone had significantly shorter duration of the second stage of labor compared to those received IM injection of 2 ml of saline. However, no statistically significant differences were found between the studied groups regarding durations of the active / first and third stages of labor. The study recommended that intramuscular injection of dexamethasone is very important to shorten the length of the second stage of labor especially for primigravidas women to prevent unwanted complications.