Objectives :The aim of this study is to evaluate the effect of intrathecal dexmedetomidine on core body temperature and shivering during spinal anesthesia in patients undergoing elective cesarean section . Design : In this double blind , clinical trail 50 patients with American Society of Anesthesiologist physical statues I or II who schedule for cesarean section will divide randomly in two equal group. Setting : After induction of spinal anesthesia patient will be covered by one layer of surgical drapes over the hole body beside head and neck during the operation and one cotton blanket in post anesthesia care unit. The temperature of operating room and post anesthesia care will be maintained in the range of 22-26 °C during study. Participants :patients undergoing elective cesarean section will be included in this study .Inclusion criteria : Filling written informed consent form , and American society of anesthesiologist physical status I or II . Exclusion criteria : any absolute or relative contraindication for spinal anesthesia , core body temperature more than 37.5 or lower than 36.5 °C , BMI>25 , cardiac block or dysrhythmia, history of Psychiatric disease , history of taking α receptor antagonist drugs , history of hypertension or taking any antihypertensive drug , history of any cardiac disease ( ischemic , valvular , block ) , history of renal failure , hepatic failure , history of allergy to study drugs , failure or incomplete spinal block , excessive hemorrhage that need transfusion . Intervention : Spinal anesthesia will be done using 12.5 Mg bupivacaine and 5 microgram dexmedetomidine in study group , and 12.5 Mg bupivacaine and 0.5 ml 0.9% Normal saline in control group . Drugs will be prepared by nurse anesthesia in equal volume (3 ml) for both group . Primary outcome : Incidence of shivering and core body temperature changes during spinal anesthesia and in post anesthesia care unit .The neonate APGAR and assessment of cardiovascular profile are the secondary outcomes of study .The core body temperature will be measure in tympanic membrane using termoscan , and in 5 minute intervals . Incidence of shivering will be evaluate by direct observation , and will be graded by 4 point scale . Cardiovascular profile including systolic and diastolic blood pressure and heart rate will be monitored continuously and be recorded in 5 minute intervals. Anesthesia complications such as hypotension, bradycardia , nausea and vomiting will be evaluate , record and treated if needed. Data will be analyzed by SPSS software , and using Chi-square test , Student's t-test, and ANOVA .