The relationship between tumor mass and peritumoral structures including peritumoral edema is important for planning surgical trajectory and crucial for diagnosis, tumor excision, and post-surgical outcome. The recent development of diffusion tensor MRI has shown its feasibility in grading tumor, monitoring therapeutic effects, and post-surgery outcome. To visualize the tumor mass and the peritumoral structure, a 3D virtual reality environment was developed. Neural tractography and peritumoral anatomy were integrated in this interaction VR system. Using a 3D controller, suitable surgical trajectory can be defined by manipulating the tumor mass, peritumoral microstructure, and brain tissues before neurosurgery. Post-surgery evaluation showed that this system was useful to design pre-surgerical plan and optimize therapeutic outcome.