The aim of this study was to determine the most suitable method for applying zinc oxide nanoparticles (nano-ZnO) to a bleached mercerized cotton textile and to enhance their adsorption on the textile surface using gas plasma to provide effective protection against ultraviolet (UV) radiation. Four methods were used in determining the most suitable method for applying nano-ZnO, which differ from each other in the application procedure, treatment time, and the content of dye or excipients in the treatment bath. Ultraviolet-visible spectroscopy (UV-Vis) and inductively coupled plasma mass spectrometry (ICP-MS) showed that white textiles treated by the exhaust method, in which the treatment bath contains double distilled water, nano-ZnO and acetic acid, have a high ultraviolet protection factor (UPF) (UPF = 30) and a high content of nano-ZnO, and that a concentration of nano-ZnO greater than 3% does not increase the UPF value. The increase of nano-ZnO absorption in the white textile was investigated under different conditions of gas-plasma treatment of the textile in a low-pressure inductively coupled plasma system, which included the gas (water vapor, oxygen, and tetrafluoromethane) and the treatment time (10, 20, and 30 seconds). The chemical and physical properties of the plasma treated cotton textile were investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The mechanical properties of the plasma treated samples were evaluated by measuring the tensile strength and elongation at break. The effectiveness of the plasma treatment was evaluated by UV-vis spectrometry and measurement of UPF. The results showed that regardless of the gas used, a longer treatment time increases the concentration of oxygen functional groups on the surface of the cotton fibers, making the surface of the fibers rougher. These two conditions are prerequisites for increasing the nano-ZnO content in the fibers, which enables excellent UPF values in treated cotton textiles. Until now, functionalized textiles showed poor wash resistance, with most of the nano-ZnO being washed out during the first wash.