This paper presents a novel method for constructing non-separable wavelet filters. The high frequency sub-bands of non-separable wavelet transform can reveal more features than that of the common used separable wavelet transform. Then, we describe a blind watermarking scheme which is based on discrete non-separable wavelet transform (DNWT). More coefficients of DNWT can add watermark than that of discrete separable wavelet transform (DSWT). Experiment results show that the DNWT watermarking scheme is robust to noising, JPEG compression, and cropping. Especially, it is more resistant to sharpening than DSWT scheme. Furthermore, by adjusting the threshold such that the number of the DSWT coefficients to embed watermark is not less than the number of the DNWT coefficients, the performance of DSWT to sharpening is still worse than the DNWT. Such adjustment also dramatically decreases the robustness of the DSWT scheme to noising.