Zinc oxide nanoparticles (ZnO NPs) was synthesized using some factors influencing ‎such as the polyethylene glycol (PEG) as a stabilizing agent at different pH and temperatures. The best conditions for preparing ZnO NPs were at pH 11, 0.1 M (7.5 mL) of PEG with molecular weights of 20000 and 60 oC.‎ Properties of synthesized ZnO NPs were confirmed using ‎different techniques (FTIR, UV-Vis, XRD, SEM and TEM). Obviously, UV-Vis spectrum of ZnO NPs showed an adsorption peak at 268 and 362 nm with a direct bandgap of 3.39 eV. ‎PL spectra of ZnO NPs showed an emission peak at 420 nm. The average sizes calculated of ZnO NPs powder using the XRD line broadening method were 19.71 nm. TEM observation showed that the prepared ZnO NPs is spherical with different diameters in the range 22.2-27.8 nm. Moreover, the ZnO NPs prepared have an excellent‎ adsorption capacity for the removal of some cations from water. The adsorption capacities were 391.6 and 437.2 mg/g for Mn(II) and Cd(II) respectively. Langmuir, Freundlich and Temkin models‎ would be well described the adsorption process. Thermodynamically, the adsorption processes of ZnO NPs were spontaneous, endothermic, and physical in nature. The good removal efficiency of Mn(II) and Cd(II) by ZnO NPs with their exceptional adsorption capability suggests that the ZnO NPs have great potential applications in environmental protection.