The influence of modifications of the ZSM-5 catalyst on the conversion of dimethyl ether to olefins is studied at low hydrocarbon conversion in order to explore the possibility of selective formation of C(4)(=)-C(6)(=). Three modifications designed in order to reduce catalyst acidity without increasing steric hindrance are compared, namely, dealumination, partial neutralization with ammonia and ion-exchange with lithium. The unmodified H-ZSM-5 produces 60 % of ethene and propene, 30 % of olefins C(4)(=)-C(6)(=) and 10 % of heavy olefins plus aromatics. In the same conversion range, the three modified catalysts promote the formation of C(4)(=)-C(6)(=) and even more the formation Of C(7)(=)-C(8)(=), and they lower the formation of light olefins and aromatics. There is only a slight difference between modified catalysts : lithium exchanged ZSM-5 leads to higher ratio of C(4)(=)-C(6)(=) to heavy by-products. An enhanced diffusivity in modified catalysts probably plays a role in the increase in the average molecular weight of olefins produced.