Background: Post-caesarean section pain is an important issue in obstetrics. Several studies have shown the importance of adequate postoperative analgesia on mobilization, rehabilitation and decreasing the length of hospital stay. Large amounts of opioid analgesic drugs are often required in the management of intense post-operative pain. However, this option is associated with many side effects. Objective: The aim of the study was to assess the efficacy of adding dexamethasone to bupivacaine for spinal anesthesia in prolonging the duration and anesthetic effect in women undergoing cesarean section. Patients and Methods: Populations of the study were comprised of 100 pregnant full term female planed for cesarean section. All patients had cesarean section under spinal anesthesia. Pain was assessed using 10 cm visual analogue scale (VAS) after 0, 15, 30 min and 2, 4, 6 hours post-operatively and until the mother asked for an analgesic. The duration of sensory block as well as postoperative analgesia were calculated. The study population had been randomized into 2 groups: The 1 st group C (n=50 women) included 50 women receiving intrathecal dexamethasone added to bupivacaine. The 2 nd group B (n=50 women) included 50 women receiving placebo which was added to intrathecal bupivacaine. Results: This study has shown that the addition of intrathecal dexamethasone to bupivacaine significantly improved the duration of sensory block in spinal anesthesia as the duration of sensory block in the study group was 122 + 7.9 minutes while in the control group it was 91.8 + 10.8 minutes and p<0.001. Also, receiving time to VAS >6 and the first analgesic dose prescription in the case group was significantly longer than that in the control group (P<0.001) as the pain free period in the study group was 434.3 + 43.8 minutes while in the control group it was 215.3 + 40.3minutes. Also, the motor block duration in the study group was significantly prolonged when compared with control group (p<0.01).There was no difference in onset time between the two groups and the addition of dexamethasone cause no complications. Conclusion: This study has shown that the addition of intrathecal dexamethasone to bupivacaine significantly improved the duration of sensory block in spinal anesthesia without any changes in onset time and complications, and has increased the pain free period statistically. Recommendations: Further studies are needed to evaluate the optimal dose of dexamethasone to be used in spinal anesthesia.