There is provided a process for reducing formaldehyde content of a gas comprising the step of contacting the gas with an aqueous oxidizing solution comprising at least one cation, a base, and H.sub.2O.sub.2 so as to oxidize at least a part of the formaldehyde contained in the gas into formic acid. Thus, a gas having a reduced content in formaldehyde as compared to the gas before the process and a solution comprising formic acid, are so-obtained. Such a process can be particularly useful for treating various types of gases containing formaldehyde.