This work numerically investigates the thermal buoyancy effect on the wake-induced vibration of a heated cylinder submerged in the wake of a stationary cylinder. Simulations are performed at Richardson number Ri = [0, 1], Prandtl number Pr = 7.1 and Reynolds number Re = 100. The downstream cylinder is elastically mounted in transverse direction with reduced velocity Ur = 4 – 20. The mass ratio is set to 2 and the damping coefficient is considered zero to attain maximum oscillation. The thermal buoyancy effect on wake-induced vibration is illustrated through flow structures, heat transfer and oscillation amplitude. Thermal buoyancy influences the flow around a cylinder and suppresses the oscillation amplitude. Multiple heated cylinders in close proximity may suffer fatigue failures or structural damage. The present findings could increase the structural durability of heated cylinders.