A lattice Boltzmann method for natural convection with multicomponent and multiphase fluids in a two-dimensional square cavity is presented. The model combines a multicomponent and multiphase method with a passive-scalar approach, which is extended to be available for multicomponent immiscible flow in this paper. It has a good computational efficiency. The natural convection of flow with two of the same immiscible fluids are simulated using the model, and the agreement with the literature data is satisfactory. A case study of natural convection with a bubble of two different immiscible fluids in a square cavity is presented to show the heat transfer in a multiphase natural convection. It also reflects the potential of the present model for simulating thermal multicomponent multiphase fluids flow with different Rayleigh numbers.