Design and construction of a new two-phase atomizer of fluid catalytic cracking (FCC) process has been studied for atomizing the heavy oil feed by steam in low pressure. This atomizer has been tested quantitatively in air-water cold system using particle dynamic analyzer (PDA). The Taguchi method of experimental design has been used to optimize the two-phase atomizer's design parameters based on the proper average droplet size and distribution. The effects of spray flow pattern (upward and downward sprays) and different distances from feed injection on droplet size and velocity distribution have been studied for optimized atomizer. © 2005 Elsevier B.V. All rights reserved.