The synthesis of dimethyl ether from syn-gas under forced composition cycling over a bi-functional copper/zinc oxide/ alumina catalyst was studied. The experiments were conducted at 270 degrees C, 2.0 M/Pa and a space velocity of 8000 h(-1). The inlet gas was switched between two compositions : H-2/CO/CO2=48/48/4 and H-2/CO/CO2=72/24/4 (both on mole basis) as square waves. The optimum split ratio and cycle period were found to be 2/3 and 3 min respectively, at which an improvement of near 30% over steady-state operation was observed in DME yield.