The behaviour and significance of interfacial viscous force on the air-water interface in a superhydrophobic microchannel are investigated numerically. The microchannel contains superhydrophobic roughness of triangular shape at the top and bottom surfaces of the microchannel. The effect of microgroove width and flow condition on the interfacial viscous force is also investigated. It is observed that the interfacial viscous force increases with increasing fluid velocity, and also an incremental characteristic is found when microgroove width is varied from 40 µm to 140 µm. Moreover, the air-water interface is found concave, flat and convex within the considered microgroove widths. The present numerical study reveals that the interfacial viscous force plays a vital role on the meniscus shape along with the Laplace pressure force and this meniscus is also important for obtaining maximum drag reduction for a particular superhydrophobic geometry.