Lots of existing image watermarking methods in Discrete Wavelet Transform (DWT) domain cannot resist lightness-adjusting attack. Therefore, a novel image watermarking method for resisting lightness-adjusting attack in DWT domain is proposed in this paper. In the method, watermark bits are embedded into DWT low frequency coefficients of original image and are extracted from the revised DWT low frequency coefficients that resist lightness adjustment of watermarked image. The method is simple and is executed rapidly and effectively. Moreover, original image is not needed when extracting watermark. Experimental results show that the method has a fine transparence of embedded watermark and is very robust to brightness-adjusting attack. Furthermore, it is strongly robust to other ordinary attacks such as re-sampling, color dithering, smoothing, noise adding, and lossy compression.