BACKGROUND Propofol is one of common anesthetic drugs used in anesthesia. The most common side effects of propofol are local pain. Pretreatment with lidocaine can reduce propofol injection pain. OBJECTIVE The aim of the present study was to assess and compare the efficiency of lidocaine 0.4% and 2% in reducing the incidence and severity of propofol injection pain. METHODS This was a double blind prospective clinical trial on children 4-8 years old with class ASA I and II candidates who were referred to Dr. Shaikh Hospital in Mashhad for elective surgery. Sample size calculated 50 patients in each groups based on pilot study. 100 children's were randomly divided equally in two groups, who were injected with lidocaine solutions 2% and 0.4% respectively. patient's pain evaluation based on VSD (verbal descriptor scale) and NRS (Numeric Rating Scale) using patient's verbal reaction and behavior namely fretting, hand drag and tearing. The collated data was analyzed. RESULTS There was nosignificant difference as to the first three variables (age, gender and weight P > 0.2). The significant difference regarding pain experience in both groups was noteworthy (P > 0.2). CONCLUSIONS Most of the studies compared lidocaine with other drugs or its efficiency at different doses. Our study is different in that we applied a constant dose of lidocaine in various volumes and concentration. This result shows that lidocaine with the same does but lower concentration and higher volume is more effective in preventing propofol injection pain. Using diluted lidocaine with the dosage of 1 mg/kg and a concentration of 0.4% is an effective way to relieve pain caused by propofol injection in children.