Interactive volume rendering methods such as texture-based slicing techniques and ray casting have been well developed in recent years. The rendering performance is generally restricted by the volume size, the fill-rate, and the texture fetch speed of the graphics hardware. For most 3D data sets, a fraction of the volume is empty, which will reduce the rendering performance without specific optimization. In this paper, we present a simple kd-tree-based space partitioning scheme to efficiently remove the empty spaces from the volume data sets at the preprocessing stage. The splitting rule of the scheme is based on a simple yet effective cost function evaluated through a fast approximation of the bounding volume of the nonempty regions. The scheme culls a large number of empty voxels and encloses the remaining data with a small number of axis-aligned bounding boxes, which are then used for interactive rendering. The number of boxes is controlled by halting criteria. In addition to its simplicity, our scheme requires little preprocessing time and improves the rendering performance significantly.