Objective　To explore the anatomic features of posterior interosseous nerve and its muscular branches to thumb and index fingers.　Methods　86 upper limb specimens from 43 fixed cadavers were used in this study. Deep branches of radial nerve were dissected, for following the courses of  posterior interosseous nerve. As well, the origin, diameter, and other anatomic parameters of its muscular branches to thumb and index fingers were measured and analyzed.　Results　Posterior interosseous nerve and its branches presented as flat and thin nerve bundles. Its main trunk and muscular branches passed between intermuscular space at posterior and middle 2/4 part of forearm. Fusiform terminal fiber enlargement appeared at the dorsal side of the wrist. The diameter of the origin of the main trunk was about（3.79±0.64）mm，except for branches to extensor digitoium with the diameter of 2.0mm, the mean diameter of other branches was less than 1.0mm. The projection line of posterior interosseous nerve extended ulnarly or radially from radial condyle of humerus to ulnar malleolus, at the supination or semipronation positions, respectively.　Conclusions　Posterior interosseous nerve and its muscular branches are easy to be damaged during its course at the middle and posterior 2/4 segment of forearm.