On-line characterization of powder and droplets during gas atomization of molten metals and alloys offers extensive opportunities for real-time process monitoring and control. The capability to make on-line measurements can significantly reduce tedious and costly powder classification, which, currently, is always carried out subsequent to the atomization process. Two laser-based particle sizing instruments, the EPCS (ensemble instrument) and PCSV (single particle instrument), were used during gas atomization of zinc with a double Coanda nozzle configuration. The laser instruments were positioned in the duct leading from the bottom of the atomization tower to the powder collection cyclone. The effect of gas to metal ratio on particle size was studied by varying the atomization gas pressure from 0.69 MPa to 1.03 MPa. Air was used as the atomizing gas for some of the 0.69 MPa runs, while nitrogen was used for all of the higher-pressure runs. Experimental apparatus and procedures for atomization and on-line powder sizing with the EPCS and PCSV are described. EPCS and PCSV measurements, which were compared with standard sieve analyses, indicate that the ensemble instrument is a good candidate for on-line process monitoring and control.