For a particular printing ink and drop-on-demand piezoelectric inkjet printhead, piezoelectric voltage and temperature of the ink were varied to change the inkjet performance, and the jetting velocity of the inkjet was analyzed under various conditions. The ink was cooled by using a Peltier module, which was attached to the nozzle plate as a heat sink. The inkjet drops were captured by the shadowgraphic method using a high-speed camera. The positions and velocities of these drops were then estimated after image processing. The drop state was distinguished by dimensionless numbers, such as the Weber and Z numbers, to decide whether it was stable for ejection and printing. Increasing the piezoelectric voltage increased the ejection velocity but with an associated generation of satellite drops. Cooling the ink increased the viscosity, which in turn decreased the drop velocity while diminishing the satellite drops. Therefore, it was shown that the cooled ink enabled stabilized inkjet ejection.