Ultrasonic atomization is conducted to produce composite particles of polyvinylpyrrolidone (PVP) and multi-walled carbon nanotube (MWCNT) from an aqueous suspension. The rheological properties of the suspensions are varied in a systematic manner by changing the molecular weight of the polymers, the polarity, and the concentration of MWCNT in the given composite system. A particular interest of this study is to investigate how the ultrasonic atomization of PVP/MWCNT suspensions is affected by their shear and extensional properties. As a characteristic of the fluid under extensional flow, the fluid relaxation time is measured from capillary breakup extensional rheometry. It is found that the average size of the composite droplets is increased as the relaxation time in the capillaries of PVP/MWCNT increases, while the number of available particles is mainly limited by the shear viscosity of the suspension. With the available materials and analyses adopted in this study, the observed trends are explained in terms of two dimensionless groups: the Deborah and Ohnesorge numbers, which encompass the material parameters (viz, relaxation time, shear viscosity, density, and surface tension) associated with the atomization process of viscoelastic fluids.