In this paper, we develop a constant-quality rate control algorithm for a surveillance system that consists of one "base encoder" for encoding a down-sampled full-view version of the input video sequence and one "region of interest (ROI) encoder" for encoding the region of interest of the input video at the original resolution. Exploiting the inter-relationship between these two independent encoders, the bits for the ROI encoder are allocated according to the distortion obtained from the base encoder. Simulation results show that the proposed algorithm significantly reduces the image quality variation. The overall quality is improved and the bit-rate is saved as compared to the rate control algorithm in JM 8.4.