The synthesis of ethylenediamine (EDA) from ethanolamine (EA) with ammonia over acidic types of zeolite catalyst was investigated. Among the zeolites tested in this study, the protonic form of mordenite catalyst (MOR) that was dealuminated by HCl (H-HCI-MOR) showed increase in activity (from 12% of conversion (H-MOR) to 52% (H-HCl-MOR)). Out of the framework of the parent MOR, around 10% of the framework aluminum was leached by the acid treatment. The reaction proved to be highly selective for EA over H-HCI-MOR, with small amounts of ethyleneimine (EI) and piperazine (PA) derivatives as the side products, compared with other processes. IR spectroscopic data provided evidence that the increase of Bronsted acid amount raised the activity and selectivity for EDA after dealumination. Along with the studies of adsorption of pyridine and ammonia, the heterogeneity of the OH band was also investigated.