A new metal polyphosphate, alpha-CsBa2(PO3)(5), exhibiting the first example of a linear P-O-P bond angle in a one-dimensional (PO3)(infinity) chain has been reported. Interestingly, alpha -> beta phase transition occurs in CsBa2(PO3)(5) along with the P-O-P bonds varying from linear to lambda-shape, suggesting that alpha-CsBa2(PO3)(5) with unfavorable linear P-O-P bonds is more stable at ambient temperature.