Zinc oxide nanoparticles (ZNPs) were prepared from Zn(NO3)2.6H2O and CON2H4. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersion Atomic X-ray (EDAX), Transmission Electron Microscopy (TEM), and Thermogravimetric-Differential Thermal Analysis (TGA/DTA) were utilized for determination of the composition, morphology, elemental analysis, crystallinity, and thermal stability respectively, while Fourier-Transform Infrared Spectroscopy (FTIR) method was used to determine the functional groups present in the ZNPs. The adsorption of Pb(II) and Alizarin Red S (ARS) onto ZNPs were investigated at different solution pH, concentration, adsorbent mass, temperature and contact time. The optimum adsorption capacity of Pb(II) on ZNPs was 341.65 mg/g at pH 10 in 180 minutes at 318 K. Similarly, the optimum adsorption capacity of ARS was found to be 18.84 mg/g at pH 4 in 180 minutes at 318 K. The Langmuir isotherm model fitted well with regression coefficient, R2 = 0.9252 and 0.9035 for Pb(II) and ARS respectively. Th pseudo-second-order kinetics with R2 = 0.9956 and 0.9549 for adsorption of Pb(II) and ARS respectively gave good fit to the adsorption processes. The ∆G◦ obtained were negative which is an indication of spontaneous adsorption processes, while the positive values of ∆H (+143.46 and +84.50 KJ/mol) and ∆S (+0.473 and +0.364 KJ/mol) for Pb(II) and ARS respectively, revealed endothermic and randomness at the ZnO-aqueous interface during the adsorption processes. The Ea were found to be +6.193 and +6.956 KJ/mol for adsorption of Pb(II) and ARS respectively which showed that the adsorption onto ZNPs is a physical process.