There is provided a process for converting methanol and/or dimethyl ether to a product containing C.sub.2 to C.sub.4 olefins which comprises the step of contacting a reaction mixture which contains methanol and/or dimethyl ether and at least 10 wt % of a polymethylbenzene component selected from trimethylbenzenes, tetramethylbenzenes and mixtures thereof with a catalyst comprising a porous crystalline material. The contacting step is conducted under conversion conditions including a temperature of about 250.degree. C. to about 500.degree. C. and a methanol and/or dimethyl ether partial pressure of about 5 to about 250 psia (35 to 1725 kPa). The porous crystalline material used in the catalyst has a pore size greater than the critical diameter of the aromatic compound and a Diffusion Parameter for 2,2-dimethylbutane of at least 500 sec.sup.-1 when measured at a temperature of 120.degree. C. and a 2,2-dimethylbutane pressure of 60 torr (8 kPa).