A　simple,　easy-to-use　approximate　equation,　in　the　form　of　a　normal　probability　distribution　function,　was　derived　for　breakthrough　curves　of　fixed-bed　reactors　or　adsorbers.　The　equation　predicts　breakthrough　curves　and　evolution　of　concentration　or　temperature　distribution　in　fixed　beds,　with　an　accuracy　higher　than,　or　comparable　to,　other　equations　previously　proposed.