Background & Purpose: In this study the effect of intravenous administration of Aminophylline on prevention of post spinal headache was evaluated. Design of experiments: double blind clinical trial Methods: Patients randomly divided into 2 groups. Inclusion criteria:140 patients candidate spinal anesthesia at the age of 18-35 and set in class I & II of Anesthesia Society of America (ASA) was selected. Exclusion criteria:Patients with history of cardiovascular disease, cerebral, Hypertension, Diabet mellitus, Preeclampsia, Seizure, Migrain, History of Post spinal anesthesia headache, Unwilling to spinal anesthesia to experience spinal anesthesia, coagulopathy,Psychiatry. Intervention: patients were randomly allocated into 2 groups recieving either 100 cc of normal salin or 1 mg/kg aminophylline dissolved in 100 cc of normal salin after delivery & cord clamping. 4,8,24,48,72 hours after operation the occurance of headache was evaluated according to VAS score.