In the paper, an automatic spatio-temporal video sequence segmentation algorithm is proposed. To address this very di cult computer vision problem, several novel algorithms have been developed which use both spatial and temporal information. First, a novel temporal segmentation algorithm is developed based on our previous work in motion estimation. Second, an iterative split-and-merge spatial segmentation scheme is proposed with an initial segmentation being provided by recursive conditioned dilation operation merging pixels into homogeneous regions, followed by an iterative re nement algorithm to obtain the nal spatial segmentation. Third, temporal and spatial segmentation are linked to form spatio-temporal segmentation with the shape of each object being simpli ed by a morphological close-opening operation to obtain the nal segmentation. Performance evaluation shows that the developed algorithm can successfully segment moving object without any human intervention.