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Zeolitic imidazolate framework ZIF-68 crystals of hexagonal rod shape were synthesized and used to study adsorption and diffusion of CO₂ on ZIF-68. Grand canonical Monte Carlo (GCMC) calculations were performed to understand the CO₂ adsorption sites on ZIF-68. Experimentally measured CO₂ adsorption isotherms on ZIF-68 can be described by Langmuir adsorption isotherm. The molecular simulation results agree well with the experimental CO₂ adsorption isotherms and heats of adsorption. The molecular simulation, coupled with the experimental isotherm data, has identified a new site between the faces of two converse nIM linkers, in addition to the two previously known sites for CO₂ adsorption on ZIF-68. Diffusivity of CO₂ on ZIF-68, obtained with a one-dimensional diffusion model, is in the range 1.1–1.6×10⁻⁷ cm²/s in 298–328 K, with an activation energy of 8.9 kJ/mol. The experimentally measured …