Disclosed is a process for producing light olefins from hydrocarbon feedstock. The process is characterized in that a porous molecular sieve catalyst consisting of a product obtained by evaporating water from a raw material mixture comprising a molecular sieve with a framework of Si--OH--Al-- groups, a water-insoluble metal salt, and a phosphate compound, is used to produce light olefins, particularly ethylene and propylene, from hydrocarbon, while maintaining excellent selectivity to light olefins. According to the process, by the use of a specific catalyst with hydrothermal stability, light olefins can be selectively produced in high yield with high selectivity from hydrocarbon feedstock, particularly full-range naphtha. In particular, the process can maintain higher cracking activity than the reaction temperature required in the prior thermal cracking process for the production of light olefins, and thus, can produce light olefins with high selectivity and conversion from hydrocarbon feedstock.