The transient process is studied in gas centrifuge cascades for separation of multicomponent isotope mixtures. Two important practical factors, the holdups in connecting pipes among separation stages and material losses, are taken into account in the partial differential-difference equations that describe the concentration distribution of components. The equations are solved at each time step through the q-iteration method. The effects on transient processes are investigated in terms of the total holdup in cascades, the cascade cut, the separation factor, and material losses and may be very significant.