Abstract: Aim: To study the morphological features of His bundle. Method: The internal architecture of His bundle were observed and measured by serial section and image analysis in 23 rats. Results: ①The rat His bundle which was 1. 08mm long could be divided into unbranching portion in the posterior (0.42mm in length) and branching portion in the anterior (0.66mm in length). ②The His bundle is composed primarily of Purkinje cell and T cell. There was not a distinct watershed but a transition area between P cell and Purkinje cell; the number of T cell gradually decreased from the mpterior to the anterior in His bundle. ③The specialized myocardial fiber was partitioned into multiple strands by fine collagen septa, which wcre main-ly longitudinally oriented. Conclusion: IXingitudinal dissociations were gradually distinct from the pesterior part to the anterior part of His bundle. Connections between fiber strands of longiludinal diwriation may be the anatomical basic of reentry.