OBJECTIVE The purpose of this study was to compare efficacy and safety of oral chloral hydrate (CH) and promethazine (PZ) for sedation during electroencephalography (EEG) in children. METHODS In a parallel single-blinded randomized clinical trial, sixty 1-10 year old children referred to EEG Unit of Shahid Sadoughi Hospital from January 2010 to February 2011 in Yazd, Iran, were evaluated. They were randomized to receive orally 70 mg/kg chloral hydrate or promethazine 1 mg/kg. The primary outcome was efficacy in adequate sedation and successful recording of EEG. Secondary outcome included clinical side effects, time from administration of the drug to adequate sedation, caregiver's satisfaction on a Likert scale, and total stay time in EEG Unit. FINDINGS Twenty four cases with mean age 2.9±1.9 years were evaluated. Adequate sedation (Ramsay sedation score of four) was obtained in 43.3% of PZ and 100% of CH group (P=0.00001). Also in 70% of PZ and 96.7% of CH group, EEG was successfully recorded (P=0.006). So, CH was a more effective drug. In CH group, EEG was performed in shorter time after taking the drug (32.82±9.6 vs 52.14±22.88 minutes, P<0.001) and the parents waited less in the EEG unit (1.29±0.54 vs 2.6±0.59 hours, P<0.001). They were also more satisfied (4.6±0.6 scores vs 3.1±1.4 scores, P=0.001). Mild side effects such as vomiting in 20% of CH (n = 6) and agitation in 6.6% of PZ group (n = 2) were seen. No significant difference was seen from viewpoint of side effects frequency between the two drugs. CONCLUSION The results of the present study showed that chloral hydrate can be considered as a safe and more effective drug in sedation induction for sleep EEG in children.