A real-time tumor tracking system has been developed for MRI-guided radiation therapy. This system allows for tumor motion to be monitored during radiotherapy and for the radiation beam to be modified to compensate for this motion. The tumor location was found during treatment through the use of a template matching algorithm and 2D cine-MR images. The tumor location information was sent to a tracking algorithm that modifies the shape of the beam in real-time to ensure the tumor target is irradiated. The tumor tracking system has been tested and found to be of submilimeter accuracy.