Resist filling process in UV-nanoimprint lithography is investigated by numerical simulation. A resist droplet on a substrate is pressed by a template and the resist flows laterally with constant velocity. The resist filling processes into the patterned cavity are simulated by various contact angles of template and substrate to the resist. Two kinds of defect modes are observed. A typical defect is induced by branching of the resist flow at the edge of the patterned cavity when the contact angle between the resist and the template is large. The other one is nonfilling into the patterned cavity for low viscosity resist and low contact angle between the resist and substrate, where the resist flows along the substrate and does not flow into the pattern.