Based on the paraffins, olefins, naphthenes, aromatics (PONA) composition of crude light gasoline, crude heavy gasoline, stabilized gasoline, and wet gas of a pilot plant fluid catalytic cracking (FCC) unit, it was found that the root cause of high gasoline olefin content and low propylene yield was low C 5 and C 6 olefin content of crude light gasoline. A new design for the main fractionater and absorber-stripperstabilizer was presented to obtain stabilized light gasoline that contains more C 5 and C 6 olefins recracked in the secondary riser. Industrial studies on the revamped unit showed that gasoline olefin content was decreased markedly, though research octane number (RON) was preserved. In addition, propylene yield was raised to a higher level and unit energy consumption (or operating cost) was not increased.