Power consumption is very critical for portable video applications such as portable video-phone. Motion estimation in the video encoder requires huge amount of computation and hence consumes the largest portion of power. In this paper we propose a novel method of reducing power consumption of the motion estimation by adaptively changing the pixel resolution during the computation of the motion vector. The pixel resolution is changed by masking or truncating the LSBs of the pixel data which is governed by an adaptive mechanism. Experimental results show that on average more than 4 bits can be truncated without a ecting the picture quality. This results in an average 70 reduction in power consumption.