Objective Inappropriate drug dosage is a serious problem in pediatrics, mainly due to the lack of clinical evidence in children, suitable preparation formulation, and standardized methods for dose adjustment. A method for evaluating and monitoring appropriate dosage in pediatrics is urgently needed. The drug utilization index (DUI) based on the Anatomical Therapeutic Chemical/Defined Daily Dose (ATC/DDD) has been widely used in the assessment of appropriate dosage in adults. We explored possible methods for assessing appropriate dosage in children. Methods Based on our previous studies, we discuss cDUI in the assessment of appropriate dosage in children as follows: the meaning of cDDD, the establishment of a standardized system, and the classified evaluation of dosage in pediatrics. Results Although the definition of cDDD draws on the concept of defined daily dose (DDD), the meaning of cDDD is different from that of the latter. Specifically, the purpose of cDDD is to evaluate appropriate pediatric dose, while DDD is a unit of measurement. cDDD could be used to assess dose rationality for common and serious pediatric diseases, and would be refined over time. A single cDDD should be assigned per drug and indication and given per drug and route of administration. The influence of age, weight, diagnosis, and administration route on the dosage should be considered. Classified evaluation should be used and weight should be given to the above mentioned factors in order to evaluate the appropriate dose objectively and comprehensively. Conclusion Dosage regulation in pediatrics has an important role in improving medical quality and protecting the safety, effectiveness, and economy of medical therapy in children. The establishment of a cDUI system is a good try in pediatric dosage evaluation. Although there are still defects within this proposed system and methodology, the principle seems feasible.