JPEG2000, the new image coding standard, is more efficient when compared with the old JPEG standard. However, most of the computations and memory usage in post-compression rate distortion (PCRD) optimization scheme in JPEG2000 is redundant. We propose an efficient rate control approach for the JPEG2000 encoder. In this approach, optimal rate distortion (RD) slope threshold is selected using the minimum RD slope of lower level horizontally and vertically low pass (LL0) subband of the wavelet decomposed image. Also, the passes of the code blocks of other subbands, whose RD slopes are less than the optimal RD slope, are skipped. The proposed approach reduces memory requirements and encoding time when compared with the existing rate control approaches for JPEG2000 standard, and also provides the same image quality as that of the PCRD approach used in the JPEG2000 standard.