The effect of Ni doping on (La_0.8Sr_0.2)_0.95MnO₃(LSM) has been studied. Ni substituted lanthanum strontium manganite,(La_0.8Sr_0.2)_0.95Mn_1-xNi_xO₃d(x-0–1.0) (LSMNix) were synthesized by ceramic route and characterized. Their crystal structure and thermal expansion behaviour have been investigated. It has been shown that the particle size of LSMNix drastically reduces with Ni substitution. The samples calcined at 900°C indicated orthorhombic symmetry where as those calcined at 1400°C were shown to berhombohedral. Compositions up to x-0.4 indicated single phase while the samples with higher Ni substitution (x≥0.5) showed formation of secondary phases such as La₂NiO₄ and NiO. The thermal expansion coefficient (TEC) of these samples increased significantly with Nisubstitution. The TEC valuesfor LSM and (La_0.8Sr_0.2)_0.95Mn_0.5Ni_0.5O_3-∂ were 10.08×10^-6 and 14.75×10^-6 °C^-1respectively in thetemperature range 25–850°C.