This paper describes a path planning method for mobile robots/vehicles be extending the path sequentially. Considering practical use and applications of the mobile robot/vehicles, additional via-points for future path are given sequentially from sensor processing and environment recognition process. Thus, the path should be calculated sequentially with such additional conditions during mission execution. In this paper, we described a key idea of our method to extend the path iteratively. Polynomial-based time curve is utilized as the basis of the method and it describes path extension segment for certain period. The coefficients of such path extension segment are renewed by additional via-points. Computer simulations with proposed method were conducted and reported for fundamental confirmations. The results shows sequential path extension can be done by our proposed method.