A small scale mechanical loading and testing device was designed and fabricated to apply in vivo loads to mouse tibiae and to mechanically test the bones in three-point bending. A linear actuator and load cell were used to apply accurately controlled forces to the samples. The device was tested and validated using standard materials of known properties to quantify accuracy and precision. The device had accuracy and precision errors of less than 5% for most of the material tests, an accuracy error of less than 10% and precision error of less than 5% for in vivo loading, and a precision error of less than 5% for ex vivo bone testing. Our results showed that the device was capable of implementing loading interventions and could be used as a tool to assess the response of these interventions. This device represents one solution to the lack of portability and a high setup cost that prevent some research groups from adopting in vivo animal loading.