Nanocolorants were prepared by miniemulsion polymerization, in which waterborne polyurethane was used as surfactant for the first time. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and dynamic light scattering (DLS) were utilized to confirm the particle diameters and particle size distributions (PSD). The results indicated that nanocolorants with relatively small particle size diameters and narrow particle size distributions could be easily prepared by this method. Simultaneously, the particle size could be controlled by adjusting the concentration of waterborne polyurethane surfactant (WPU), and the obtained nanocolorants exhibited high stability against electrolyte, lightness, and strong color depth owing to the nanoscale effects of the nanocolorant particles. Furthermore, the prepared nanocolorants achieved superior migration fastness and good thermal stability.