"Sinew" is a traditional Chinese medicine （TCM） concept， which belongs to the “five-body constituents” category and is crucial in the clinical treatment with Tui na. The meaning， types， distribution law and diagnosis and treatment value of “sinew” were summarized by reviewing representative ancient pediatric books in Ming and Qing dynasties， including

Secret Transmissions of Manipulation of Managing Frightening and Pinching Sinews

（《秘传看惊掐筋口授手法论》），

Classic of Children Massage

（《小儿按摩经》），

Secrets of Children Tuina

（《小儿推拿秘旨》），

Corrected Massage Essentials

（《厘正按摩要术》），

Secret Book on Pediatric Tuina

（《幼科推拿秘书》），

Iron Mirror on Pediatrics

（《幼科铁镜》） and

The Grand Compendium of Pediatrics

（《幼幼集成》）. It is found that "sinew" has the meaning of veins， acupoints， one of the five body constitutions， and tissue connecting joints and muscles in the ancient pediatric books. On this basis， the theory of six sinews was analyzed， and the inner connection and theoretical significance of the six sinews and certain acupoints and manipulations were explained. Simultaneously， this paper summarized the functions of six sinews in guiding syndrome differentiation in TCM as well as in regulating yin and yang， harmonizing zang-fu （脏腑） organs， suppressing fright and arresting convulsion， with the aim of using the concept of “sinew” to better guide the clinical practice of pediatric tuina.