Nb-related perovskite oxides, such as NaNbO₃, KNbO₃, and AgNbO₃, are the end members of novel ferroelectric materials. Although they have NbO₆ octahedron, the phase transition mechanism changes depending on A-site ion. NaNbO₃ and KNbO₃ have rhombohedral structure at low temperature, and after the structural phase transition, orthorhombic structure appears. On the other hand, the monoclinic structure of AgNbO₃ appeared as a disordered phase of rhombohedral structure. The rhombohedral structure is a highly ordered average structure, and the rhombohedral structure also tends to be subject to the influence of local randomness. We performed local structure analysis by using atomic pair-distribution function (PDF) and X-ray absorption fine structure (XAFS). Although these three materials have perovskite structures in which Nb occupies to B-site, local structures differ greatly. The Nb-O bond distribution appeared clearly in NaNbO₃, but broaden in AgNbO₃. The difference of local structures causes various phase transitions of Nb-related perovskite materials.