Recently, Ni11(HPO3)8(OH)6 material was reported as a bifunctional oxygen evolution reaction/hydrogen evolution reaction catalyst for electrochemical overall water splitting with unexpected structural stability and enhanced durability in alkaline media [1] or as possible candidate for aluminium-ion batteries [2]. The crystal structure of the nickel phosphite phase is characterized by a complex 3D framework with double chains of edge sharing Ni2+ 2O9 dimers running along the c-axis and noncentrosymmetric space group (P63mc) [3]. In this work, we report the study of thermal behaviour for nickel phosphite materials up to 800oC in air atmosphere by TG analysis. In the present study is established that the nickel phosphite is structural stable up to ≈400oC in air and at 800oC the Ni3(PO4)2 phase is formed. The compound has been syntesized by high-pressure hydrothermal synthesis and the morphology is presented as spherical urchin-like superstructures formed from nanorods having a mean diameter of ≈50 nm [4]. The specific surface area of the particles, FT-IR analysis and magnetic measurements for the samples will be presented.