More viscous fuels such as residual oil tend to be burned in boilers. However, the use of high viscous fuels in conventional plants will degrade combustion characteristics, such as combustion efficiency and emission characteristics, which greatly depend on the fuel spray characteristics. The present study investigated the effects of the fluid viscosity and the atomizing air flow rate on the spray characteristics of a Y-jet atomizer. The test liquid and atomizing gas were aqueous glycerol solutions and air, respectively. Spray shape was visualized at different axial positions by using short-exposure backlight method. Droplet size and velocity were measured by a Phase Doppler Particle Analyzer (PDPA).The results show that the spray shape was similar to hollow-cone regardless of viscosity and air flow rate. Spatial distribution of total droplet volume measured by PDPA per minute had the maximum value at the opposite side of test liquid supply line. The largest Sauter mean droplet diameter (SMD) existed at the side of test liquid supply line. SMD increased with the test liquid viscosity. On the other hand, as the atomizing air flow rate was increased, SMD decreased.