This article aims to present an improved technique for the mechanical characterization of single plant fibers. In particular, our efforts lie in resolving the difficulties involved in the testing of short plant fibers with only a few millimeters in length and tens of microns in width. Such fibers are potentially used as reinforcement phase in polymer composites. A special fiber gripping system, consisting of a pair of fiber clamps, a 3D positioning stage and two digital microscopes, was developed and combined to a small commercial mechanical tester. The resultant testing system possesses great convenience and reliability for the installation, orientation adjustment, and gripping of short plant fibers, as well as powerful control and data analysis functions. The equipment was then applied to the mechanical characterization of single bamboo fibers under air-dried state. Furthermore, the capability of this equipment for studying moisture content-related mechanical and viscoelastic properties of bamboo fibers was also successfully demonstrated.