A series of samples were prepared by treating HY zeolites with NH3 under high temperature. Their structures, acidity and basicity as well as the coke contents after reaction were systematically characterized by means of XRD, elemental analysis, 29Si MAS NMR, NH3-TPD, CO2-TPD and TG techniques. Their catalytic performances in the formaldehyde–isobutene Prins condensation were evaluated. The effects of samples nitridated under different atmosphere and reaction conditions were investigated in details. It is found that the selectivity of 3-methyl-3-buten-1-ol (MBO) increases to 89% and its yield is up to 82% on catalyst nitridated with NH3 containing 5% water under the optimized reaction temperature of 230 ℃ and reaction time of 4 h. Moreover, the coke contents decrease obviously from 27% on HY zeolite to 4.3% on nitridated sample after reaction. The acidity and basicity characterizations of the samples indicate that treating HY zeolites with NH3 leads to the decrease of the acidic sites and increase of the medium-strong basic sites, which inhibits the side reactions and enhances MBO selectivity. Meanwhile, the coke content decreases obviously on the nitridated sample due to its fewer acid sites and appropriate amount of basic sites.