Objective To determine the extent of off-label drug use in pediatric outpatients of West China Second University Hospital in 2010, and to analyze its possible risk factors, so as to provide baseline data for getting acquainted with the extent of off-label drug use in pediatrics in China and developing policy of off-label drug use. Methods The stratified random sampling was conducted to select prescriptions of children aged 0 to 18 years in pediatric outpatients of the West China Second University Hospital in 2010. According to drug instructions, off-label drug use of prescriptions of all selected children was analyzed in the following aspects, the category of off-label drug use, age, category of drugs. In addition, an analysis was conducted to check the relationship between off-label use and following possible risk factors: age, sex, essential medicines and over-the-counter drugs. Results A total of 2 640 prescriptions with 8 588 medical advices involving 329 drugs were extracted and analyzed, with incidence rates of off-label drug use accounting for 76.59%, 40.88% and 83.89%, respectively. The main categories of off-label drug use were no pediatric information (35.57%), indication (25.44%), and dosage (25.31%). The top 2 age groups with highest incidence rate of off-label drug were neonates (54.35%) and adolescents (49.64%). The top 4 drugs with highest incidence rate of off-label drug were respiratory system medicines (48.12%), Chinese patent medicines (48.12%), digestive and metabolic system medicines (33.36%), and systemic anti-infectives (16.27%). The off-label use risks in all age groups in the hospital were indifferent, and the essential medicines and prescription medicines were likely to present higher risks of drug off-label. Conclusion Off-label drug use in pediatric outpatients is common with growth trend in pediatric outpatients of the West China Second University Hospital. On the one hand, drug instructions lack pediatric information, and on the other hand, it’s badly in need of developing relevant legislation, regulations or guidelines to regulate off-label drug use, providing more evidence by conducting clinical trials on pediatric drugs, encouraging the development and production of the applicable drugs and dosage forms for children, and establishing the children essential medicine list, so as to avoid doctor’s professional risk and ensure the safety of pediatric drug use.