An improved process for fluid catalytic cracking or hydrocarbons employing a Y zeolite in a silica-alumina matrix and containing from about 0.1 to about 5 weight percent fluorine. The catalyst is prepared by contacting a Y zeolite in a silica-alumina matrix with an aqueous solution of a fluorine compound, preferably an aqueous solution of hydrogen fluoride, for a period of 16 to 24 hours, followed by drying and calcining the resultant fluorided cracking catalyst. The process of cracking hydrocarbons with these catalysts produces improved yields of motor fuel fractions of improved octane number as compared with processes employing unfluorided cracking catalysts.