Catalysts are playing an important role in the petroleum refining industry. The improvements of the refining processes are usually related closely to the developments of the refining catalysts. New processes could produce high quality products and reduce manufacturing cost because of the continuous remodelments of the catalysts applied. The applications of the refining catalysts in practical refining processes have exceeded for over half century. The development in the field of the carriers and active sites’ study of various kinds of catalysts have achieved magnificent results by the researchers, the refiners can apply the catalysts which are most stable (with high activity and selectivity) and less environmental pollution to produce the expected products. This article describes in detail the catalysts applied in different petroleum refining processes with a hope to show the readers about a complete outline that can be a reference when purchasing new catalysts