The effects of bed geometry on heat transfer and particle behaviors of gas-solid fluidized bed reactor for CO2 capture was investigated. Computational fluid dynamics(CFD) technique using Eulerian-Eulerian approach was used to simulate the particle motion and heat transfer characteristics in a gas-solid fluidized bed reactor. In order to comparatively analyze the effect of bed geometry, simulations of reactor having various cross section shape were carried; circular, square and different rectangular of different aspect ratio. The results indicated that particle behaviors and heat transfer characteristics depended on bed geometry. The particle downflows near the wall of circular reactor was uniform, but, those of square and rectangular reactors was non-uniform. As aspect ratio of rectangular reactors increased, uniformity of the particle downflows was decreased. Bed-to-wall heat transfer characteristics varied depending on the bed geometry. In rectangular reactors, there was the different in bed-to-wall heat transfer coefficient between the large surface and the small surface