A process for the removal and recovery of mercury and, if desired, other heavy metals from incinerator waste water produced by washing waste gases from incinerators, which comprises adding to the waste water a reducing agent or a combination of oxidizing and reducing agents, subjecting the thus added waste water to stripping treatment in the presence of ferrous ion to obtain a mercury vapor-containing gas and simultaneously form spinel type crystalline compounds and then cooling said gas to separate and recover the mercury. If desired, said spinel type crystalline compounds are also removed from the mercury-free waste water.