Amorphous phosphates are very important for potential applications in optical communications and laser technologies [1, 2], and recently, in ultraviolet (UV)ray shielding from sunshine [3]. In our previous paper, we have developed a series of amorphous cerium– titanium pyrophosphates (Ce1−x Tix P2O7; x = 0–1) for UV-shielding materials [3]. These phosphates take full advantage of the amorphous state to attain effective UV shielding, and thus the feature characteristics deteriorate when the amorphous phosphates crystallize. Therefore, it is significantly important to stabilize the amorphous state in order to maintain the UV-ray shielding effect steadily. In the series of amorphous Ce1−x Tix P2O7 phosphates, CeP2O7 and Ce0.5Ti0.5P2O7 can maintain the amorphous state up to 773 and 923 K, respectively [4–6]. However, TiP2O7 crystallizes even at 673 K, which is the lowest crystallization temperature among the Ce1−x Tix P2O7 phosphates [6]. It is necessary to develop amorphous titanium phosphate, thermally stabilized above 673 K in order to apply the material to heat-stable paints, plastics and films or UV protection suits for welders. In this study, therefore, we aim to enhance the thermal stability of the amorphous TiP2O7 by doping niobium and tantalum as stabilizers, because the Nb and Ta ions have the same positive charge (5+) to phosphorous and can form amorphous phosphate easily [7]. Amorphous TiP2O7 was prepared by the coprecipitation method [3–5], and stabilization of the amorphous state was achieved by substituting phosphorus ion to niobium or tantalum ion in the amorphous phosphates in the ratio of 10–40 mol%. A titanium(IV) sulfate solution (30%) was dissolved in deionized water, adjusting the titanium concentration to be 0.1 mol dm−3. An ethanol solution containing niobium chloride or tantalum chloride solution in a concentration of 0.05 mol dm−3 was also prepared. The titanium(IV) sulfate solution and a 0.1 mol dm−3 of sodium pyrophosphate aqueous solution were simultaneously dropped into the ethanol solution in the stoichiometric ratio. The resulting precipitates were separated by centrifuging, successively washed with deionized water for five times, and dried in an oven at 353 K for 24 hr. In order to evaluate the thermal stability of the amorphous phase, samples were calcined at 473–973 K for 5 hr at a heating rate of 100 K min−1.