Microscopic visualization can provide valuable information to enhance the understanding of pore-scale transport phenomena. Micromodels are artificial models of porous media that can be used to simulate transport processes at the pore scale. Previous micromodel studies focused mostly on pore-scale observation of immiscible fluids. In this study we observed and modeled solute transport in a horizontally mounted micromodel with a regular geometry of orthogonal channels. Dye solutions were injected as tracers at a constant flow rate to observe the solute transport with time. Images were video recorded and processed with an image analyzer to obtain the concentration contours of the solute front. Solute transport was also observed at point, pore, and REV scales through a microscope. Following the determination of micromodel porosity and hydraulic conductivity, we presented a methodology to calculate micromodel dispersivity based on REV-scale breakthrough curves measured at three different points along the micromodel centerline. Experimental values were compared with the numerical results of an advective-dispersive solute transport model which treats the micromodel as a macroscale porous medium. Furthermore, we employed a two-dimensional discrete fracture model in which the network of channels is treated as a set of mutually orthogonal fractures in a nonporous medium. The simulation results compared favorably with experimental observations processed by an image analyzer.¿ 1997 American Geophysical Union