This study was carried out to investigate the precipitation behavior of the ${chi}$ phase and the impact toughness of 25%Cr-7%Ni-2%Mo-4%W super duplex stainless steel. The ${chi}$ phase was precipitated in the early stage of aging, and with the increasing aging time. However, after reaching a maximum value, the number decreased as a result of the gradual transformation of the ${chi}$ phase into the ${sigma}$-phase. It was proved that the ${chi}$ phase was an intermetallic compound, which represented a lower nickel concentration, higher chromium and molybdenum concentrations, and very higher tungsten concentration compared to the matrix phases. It also showed higher molybdenum and tungsten concentrations than the ${sigma}$ phase. The decomposition of the ferrite phase into the ${gamma}_2$ and ${sigma}$ phases was retarded by W substitution for Mo. Thus, the number of ${chi}$ phases increased. The impact value was decreased by the substitution of W for Mo. The impact toughness rapidly decreased with time when the ${chi}$ phase began to precipitate in the initial stage of aging. The impact toughness was, therefore, greatly influenced for the precipitation of the ${chi}$ phase.