In this study, the morphological effects of ZnO on the antimicrobial and deodorant activities of synthetic fibers were investigated. Three different polyethylene terephthalate (PET)/ZnO filaments were prepared by incorporating various ZnO nanostructures (rods, plates, and spheres) into PET filaments via a melt-spinning process. The antimicrobial activity of the as-prepared fibers was evaluated by the shake-flask method using two types of bacteria (Staphylococcus aureus and Klebsiella pneumoniae). The deodorant activity of the as-prepared fibers was evaluated by the gas detection tube method. All the PET/ZnO filaments exhibited excellent antimicrobial activity with a bacterial reduction value of 99.9%. The PET/ZnO rod filament showed the best deodorant performance of 60.0%. Both the antimicrobial and deodorant activities of the PET/ZnO filaments were influenced by the morphology of ZnO. However, the morphology of ZnO had a different effect on each functionality of the PET/ZnO filaments. The antimicrobial activity of the PET/ZnO filaments was mainly affected by the physical properties of ZnO rather than its morphology. By contrast, the deodorant activity of the PET/ZnO filaments was highly influenced by the morphology of ZnO.