A 3D printing apparatus includes a substrate stage configured to support a substrate, a droplet ejector including at least one droplet nozzle configured to discharge a photo-curable droplet on the substrate, a first photo curing unit configured to irradiate light to a drop path along which the droplet discharged from the droplet nozzle falls to change a viscosity of the droplet, and a second photo curing unit configured to irradiate light onto the droplet that has landed on the substrate to cure the droplet.