In the joint scalable video model (JSVM), selection of quantization parameters for mode decision (QPMD) and bit rate control (QPBC) is important for efficient coding performance. For quality (SNR) scalability, QPMD is adjusted only to the base layer QPBC in JSVM. Thus, it reduces coding efficiency in the enhancement layer. In this paper, we propose a new method for selecting optimum quantization parameters for mode decision (OQPMD) in order to improve coding efficiency for both the base and the enhancement layers. For the base layer, we propose optimum scaling factors in each decomposition stage. We also propose an offset quantization parameter for the enhancement layer. Experimental results show that the proposed method increases the average PSNR value up to 0.8dB.