In ITS(Intelligent Transportation System), on-road object detection algorithm is one of the most important research fields and obstacle segmentation is a key factor in obstacle detection approaches. In this paper, a simple and fast segmentation approach is proposed for on-road object in ITS. Firstly, a simple method is applied to detect the interest pixels in the transportation scene images by the defined interest pixels function and a single strategy is applied to reduce the redundant computation in the process of computation gray mean of pixels in squared window; Secondly, all the detected interest pixels neighbored each other are grouped to object interest region; after that, the non-interest pixels enclosed by interest region are changed as interest pixels; Lastly, the binarized images can be easily segmented applying simple edge detection algorithms or contour tracing approaches. Several images captured from ITS system is used to test the proposed algorithm, the result indicate that the approach is valid and feasible.