A process for increasing the yield of C3 olefin in fluidized bed catalytic cracking of hydrocarbon feedstocks is disclosed. C4 fraction produced from the cracking of hydrocarbon feedstock in the primary reaction zone (riser), optionally with external source of C4 stream is fed into the stripper which acts as a secondary reaction zone at an elevated temperature and at an optimum WHSV. The elevated temperature is achieved by injecting a part of the regenerated catalyst from regenerator, which is at a higher temperature, directly into the stripper through a dedicated additional lift line. This raises the activity of catalyst inside the stripper. The direct injection of regenerated catalyst into the stripper, besides producing higher yields of propylene, improves the stripping efficiency leading to enhanced recovery of strippable hydrocarbons.