Particle-resolved direct numerical simulations (PR-DNS) of a simplified experimental shallow fluidized bed and a laboratory bubbling fluidized bed are performed by using immersed boundary method coupled with a soft-sphere model. Detailed information on gas flow and individual particles' motion are obtained and analyzed to study the gas-solid dynamics. For the shallow bed, the successful predictions of particle coherent oscillation and bed expansion and contraction indicate all scales of motion in the flow are well captured by the PD-DNS. For the bubbling bed, the PR-DNS predicted time averaged particle velocities show a better agreement with experimental measurements than those of the computational fluid dynamics coupled with discrete element models (CFD-DEM), which further validates the predictive capability of the developed PR-DNS. Analysis of the PR-DNS drag force shows that the prevailing CFD-DEM drag correlations underestimate the particle drag force in fluidized beds. The particle mobility effect on drag correlation needs further investigation. (C) 2016 American Institute of Chemical Engineers