AbstractLiquid fluidization of mixtures of solid particles of spherical and cylindrical shape has been numerically simulated. The simulations explicitly resolve the solid–liquid interfaces by means of an immersed boundary method implemented in a lattice‐Boltzmann flow solver. A soft collision algorithm deals with particle–particle contacts and close‐range hydrodynamic interaction. The systems studied have an overall solids volume fraction of 0.40, with 5%–35% of the overall solids volume contained in the cylinders. One focus of the study is on the effect of the length over diameter aspect ratio (that has been varied between 4–10) of the cylinders on the co‐fluidization behaviour. The average slip velocity of the cylinders only weakly depends on the fraction of the cylinder volume in the solid particle mixture. The cylinders do stir the system, with velocity fluctuation levels increasing if the number of cylinders relative to the number of spheres is increased. When co‐fluidized, the taller cylinders preferentially orient vertically, as they also do in cylinder‐only fluidization.