The coupling conversion of methanol and C-4 hydrocarbon (62.2 wt % of n-butanes and 34.4 wt % of n-butylenes) to propylene was studied over La-modified HZSM-5 (La/HZSM-5) catalysts. Compared with the individual methanol to olefins and C-4 hydrocarbon cracking to propylene, the coupling conversion remarkably improved propylene yield and the catalytic stability of La/HZSM-5. In the coupling conversion, propylene yield was strongly dependent on the reaction conditions and the loading of La. The interaction of La with hydroxyl groups (OH) adsorbed on HZSM-5 surface occurred. Such interaction modified the density and distribution of add sites from the hydroxyl groups. Propylene yield was close relative to the density and distribution of acid sites. The comparatively high propylene yield of ca. 46.0 wt % was obtained on La/HZSM-5 catalyst with 1.5 wt % load of La (1.5 wt % La/HZSM-5), possibly due to the moderate density and distribution of acid sites on the catalyst.