A series of experiments have been performed to find out the effect of the mixing port length of Y-jet atomizers on the spray performance, using air and water as the test fluids. Water and air flow rates and the drop sizes were measured. Variation of the air flow rate with change of the mixing port length was insignificant. However, the water flow rate was very much susceptible to the mixing port length. Mixing point pressure was found to be very much influenced by the mixing port length. Flow pattern of the air/water mixture inside the mixing port was postulated through the experimental observations; and the variations of spatial distribution of Sauter Mean Diameter(SMD, D32) and the cross-section-averaged SMD(D32m) with different mixing port length and air/water mass flow rate ratio were examined. Generally, the mean drop size decreased and became spatially even when the mixing port length was reduced. Tentative correlations showing the mixing port length effect on the mixing point pressure and the cross-section-averaged drop size were provided.