Hyperbaric bupivacaine is the most common drug used in spinal anesthesia for caesarean section. The aim of this study was to compare the effects of adding fentanyl to intrathecal bupivacaine on the onset and duration of spinal anesthesia and its effect on mother and neonate. Seventy healthy parturients with singleton pregnancy scheduled for elective cesarean section were randomly allocated to receive subarachnoid block with 0.5% bupivacaine heavy 2.4 ml (Group A) or fentanyl 20 microgram (0.4 ml) added to 0.5% bupivacaine heavy 2 ml (Group B). Blood pressure, heart rate, respiratory rate, oxygen saturation, along with characteristics of spinal block were assessed throughout the surgery and in the postoperative ward until the patient requested for analgesia. It was found that duration of sensory block was prolonged in fentanyl group (p < 0.05). Duration of complete analgesia (97 ± 8.23 minutes vs 153 ± 7 minutes; p value = 0.00) and effective analgesia (134 ± 5.6 minutes vs 164 ± 9; p value = 0.00) were also found to be prolonged in Group B. There was not much difference in the occurrence of side effects in both the groups. Addition of fentanyl to intrathecal bupivacaine for cesarean section increases the duration of postoperative analgesia without increasing maternal or neonatal side effects.