Microfluidic devices could find applications in many areas, such as BioMEMs, miniature fuel cells and microfluidic cooling of electronic circuitry. One of the important considerations of microfluidic device in analytical and bioanalytical chemistry is the dispersion of solute. In this study, we have developed an analytical solution, which considers the axial dispersion of a solute along the flow direction, to simulate convection and diffusion transport in a pressure driven creeping flow for a rectangular shape slit. During flow, the balance of competing effects of diffusion (especially cross-section diffusion) and convective diffusion in the flow direction are investigated. / Singapore-MIT Alliance (SMA)