This invention relates to a process of producing C2- to C4-olefins from steam and a feed mixture containing C4- to C8-olefins, wherein the feed mixture containing steam is introduced into a reactor with an inlet temperature of 300 to 700 C., said reactor comprising a bed of granular, form-selective zeolite catalyst, and wherein a product mixture containing steam and C2- to C4-olefins is withdrawn from the bed and is passed through at least one cooling means.