The aim of this randomized double blind clinical trial is reducing usual dose of bupivacaine for spinal anesthesia by adding fentanyl. Can be reducing common side effects of bupivacaine (hypotension), this result in an appropriate level of anesthesia in patients. 105 pregnant women (18 to 40-year-old) candidate for elective cesarean section with spinal anesthesia entered the study. Who had singleton term pregnancies in class I physical health classification of the American Society of Anesthesia (ASA).And mothers with a history of hypertension, diabetes, cardiovascular and cerebral diseases, known fetal anomaly, any kind of contraindications for spinal anesthesia and those with difficult tracheal intubation were excluded. They were randomly divided into three groups of 35 women. The first group received 10 mg of bupivacaine 0.5%, the second received 8 mg of bupivacaine 0.5% with 25 microgram of fentanyl, and the third received 8 mg of bupivacaine 0.5% with 0.4 ml of normal saline Intrathecally. Blood pressure, heart rate, sensory level, degree of motor block, pain score during operation, nausea and vomiting, time taken to recover from sensory and motor block were measured and compared in three groups during and after surgery. Our data will be analyzed using the using t-test, Mann-Whitney test and Chi-square tests. A P value <0.05 will be considered statistically significant.