BiNiO₃ is a perovskite compound with a triclinic crystal structure and an unusual oxidation state of Bi³⁺_0.5Bi⁵⁺_0.5Ni²⁺O₃ at ambient condition. Partial substitution of La³⁺ for Bi destabilizes the charge disproportionation of Bi into Bi³⁺ and Bi⁵⁺ and orthorhombic (Bi, La)³⁺Ni³⁺O₃ state appears at high temperature. Because of the shrinkage of the Ni – O bond length, the high-temperature phase has smaller volume. The coexistence of both phases changing their fractions in Bi_0.95La_0.05NiO₃ leads to a negative thermal expansion (NTE) with a dilatometric thermal expansion coefficient of − 82 × 10⁻⁶ /K, three times as large as the existing compound. This phenomenon is generally observed in Bi_1−xLn_x NiO₃ (Ln: lanthanide ions). NTE is also expected for BiNi_1−xM_xO₃ (M: trivalent ions) because Ni substitution with other trivalent ion stabilizes Bi³⁺(Ni, M)³⁺O₃ state. The presence of 50 K hysteresis between the heating and cooling cycles of Bi_1−xLn_x NiO₃ owing to the first order nature of the transition might be a problem for the practical application. From an analogy to relaxer ferroelectrics, suppression of the temperature hysteresis is also expected for BiNi_1−xM_xO₃. BiNi_1−xFe_xO₃ samples showed NTE with reduced hysteresis compared with Ln substituted samples. This result strongly suggests that the phase transition is approaching to the second-order like.