This paper proposes the blind watermarking algorithm for digital video based on magnitude modulus subband in wavelet transform domain. After transforming each of frames into wavelet domain, the proposed algorithm divides LH, HL, and HH subbands of 2-level into $3{ imes}3$ blocks and calculates average magnitude modulus of all blocks. Then the watermark bit is embedded into a target magnitude modulus comparing with an average magnitude modulus within a block. Experimental results were confirmed that the proposed algorithm has the good robustness against MPEG and frame attacks than the conventional algorithm.