Aims: This study aimed to comparatively investigate the efficiency of removal of formaldehyde using advanced oxidation process ultraviolet (UV)/S2O82-/Fe2+ and UV/S2O82- from aqueous solutions. Materials and Methods: In this experimental-laboratory study, the UV/S2O82 and UV/S2O82-/Fe2+ processes were used to remove formaldehyde. UV radiation was provided by a low pressure (6 W) UV lamp. Effects of various factors including pH, different irradiation durations, different concentrations of iron ions, initial concentration formaldehyde, and persulfate concentration were evaluated. The remaining formaldehyde concentration in the samples was measured by spectrophotometer at 412 nm wavelength. Results: The results showed that in the UV/S2O82- method, the formaldehyde removal efficiency decreased with increasing pH from 3 to 9, while in the UV/S2O82-/Fe2+ method, the formaldehyde removal efficiency increased with increasing pH and concentrations of iron ion. In both methods, as the initial concentration of formaldehyde was increased, its removal efficiency decreased, and the highest formaldehyde removal rate was obtained in UV/S2O82- method at persulfate concentration of 100 mM. However, in the UV/S2O82-/Fe2+ method, the removal efficiency decreased with increasing concentration of persulfate to 100 mM. Conclusion: The results showed that the UV/S2O82-/Fe2+ process was more efficient (87.57%) to remove formaldehyde at high concentrations. Therefore, it is recommended to study the efficiency of this process as one of the clean and environmentally friendly methods at full scale for real wastewater.