Based on depth image based rendering (DIBR), this paper presents an efficient hole-filling approach using adaptive rendering for the 2D-to-3D conversion system, i.e., converting monocular image to multi-view virtual images. The traditional processing of DIBR includes depth map pre-processing, image 3D warping, and hole-filling. The depth map pre-processing stage is mainly dedicated to reduction of holes, but it will bring about geometric distortion and texture artifacts. Therefore, an efficient hole filling approach without the depth-map preprocessing is motivated for enhancing the quality of multi-view virtual images. The adaptive rendering strategy is employed to find the appropriate block for performing hole-filling process. Experimental results show that the proposed approach is superior in hole-filling ability to other methods.