Conversion reaction of 1-butene over phosphorus-impregnated HZSM-5 zeolite was studied. The effect of phosphorus impregnation was discussed with the product distributions observed at various conditions of reaction temperature and partial pressure of 1-butene. The initial product distribution can be explained by the reaction path based on the formation of octene or dodecene from two or three molecules of 1-butene via cracking to smaller olefins. activities for the cracking of pentanes and hexenes and for the dehydrocycliza-tion to aromatic formation were reduced by the phosphorus impregnation. These effects were explained by the reduction of catalytic activity for cracking and dehydrocyclization of olefin.