Disclosed is a process of preparing aromatic hydrocarbons and liquefied petroleum gas (LPG) from a hydrocarbon mixture, in which a non-aromatic compound in the hydrocarbon feedstock mixture is converted into a gaseous material having a large amount of LPG through hydrocracking, and an aromatic compound therein is converted into an oil component having large amounts of benzene, toluene, and xylene (BTX) through dealkylation and transalkylation, in the presence of a catalyst obtained by supporting platinum/bismuth onto a mixture support having zeolite and an inorganic binder. The gaseous product is separated into LPG and a mixture of methane and ethane depending on differences in boiling point through distillation, while the liquid product is separated into benzene, toluene, xylene, and C9+ aromatic compounds depending on differences in boiling point through distillation.