Couette flow of a Casson fluid in an inclined composite duct comprising of porous and fluid layers of different thickness is investigated. A fully developed steady flow is assumed to be produced by applying a constant pressure gradient. The flow governing equations are described as per the standard literature. The boundary conditions at the porous and free fluid interface are formulated and the equations for fluid velocity within the porous layer and in the open channel are solved analytically. These flow quantities are studied for the effect of parameters such as porous layer thickness, volume fraction of fluid, viscosity parameter, drag parameter, angle of inclination, upper plate velocity and Casson fluid parameter. The results obtained are compared with standard literature and show good agreement. The study reveals that under prescribed conditions fluid flux in the porous layer is higher than that of in the open channel.