A catalytic conversion of ethanol to propylene was carried out by use of H-ZSM-5 with Si/Al-2 ratio of 280. In H-ZSM-5 modified at a molar ratio of La to Al-2 of 2.2, the propylene selectivity was 31% at 0.1 MPa, 550 degrees C and was higher than those of non-modified and other metal modified catalysts. In the La-modified H-ZSM-5, a rapid increase in ethylene formation was also depressed and the propylene selectivity was still high (24%) even after 28 h-reaction.