Spinal anesthesia (SA) may impair thermoregulatory control, which may result in shivering, which is a potentially harassing complication. The aim of the current study was to evaluate the prophylactic effects of intravenous ketamine on the prevention of shivering in patients who underwent elective cesarean section (CSs) under SA. In this double-blind, randomized placebo controlled trial, a total of 90 parturients under SA using hyperbaric bupivacaine 12.5 mg were allocated in two groups to receive ketamine 0.3 mg/kg or 0.9% saline following delivery. After induction of SA, patients were observed for the incidence and intensity of shivering using a four-point scale. Shivering was observed in 24 patients (53.3%) in the saline group and 15 patients (33.3%) in the ketamine group. Median (quartiles 1 and 3) of the intensity of shivering was 1 (0-2) and 0 (0-2) in saline and ketamine groups, respectively. Time from spinal anesthesia to the beginning of shivering was 33.1±11.7 min in saline versus 41.6±20.7 min in the ketamine group. The incidence of nausea, vomiting, hypotension, and bradycardia was not different between the groups. A significantly higher incidence of nystagmus and sedation was observed in the ketamine group when compared with the saline group administration of low dose i.v. Ketamine (0.3 mg/kg) was effective in lowering shivering intensity during CSS under spinal anesthesia, though side effects such as nystagmus and sedation may restrict its effectiveness.