The electron mobility values have been obtained in n-ZnO at 77 K using the Monte Carlo simulation technique. The values agree satisfactorily with available data. The mobility values thus obtained have then been expressed by simple power law relationship. It is observed that the mobility values calculated by using these simple power law relations yield values that show agreement within 5% with those obtained from the detailed Monte Carlo simulation technique. We conclude that such empirical relationships can be effectively used for quick determination of mobility values at different electric fields in a device-modelling program and in the development of CAD tools.