In textile inkjet printing, understanding the effect of viscosity and surface tension of a reactive dye ink on droplet formation is of great significance. As an organic ecofriendly solvent, polyethylene glycol with a molecular weight of -400 g/mol (PEG400) was used to prepare reactive dye inks with or without Surfynol 465 (S465) to explain separately how viscosity and surface tension affect the droplet formation of a reactive dye ink. The intermolecular interactions in the ink and physical properties of the ink were investigated by measuring the visible absorption spectra, hydrodynamic radius, viscosity, and surface tension. Droplet formation under a single variable influence of viscosity or surface tension was observed by taking photographs using a high-speed camera. Results show that a high ink viscosity condition generates no satellite droplet formation and a slower droplet velocity, and a higher surface tension tends to cause ligament rupture from the nozzle tip and the droplet. Moreover, a twill cotton fabric printed using the PEG-S465-dye ink at a 30% PEG400 concentration showed higher ink penetration, dye fixation rate, ideal color strength, and rubbing fastness.