We have deposited Mn on the (110) surface of Ni and discover ordering into a c(2 × 2) superstructure for coverages of 0.35-0.5 monolayer Mn. Mn 2p photoemission spectra show distinct satellite structures which disappear for higher Mn coverage. Calculations using configuration-interaction theory including multiplet effects on a model cluster representing the local geometry of a surface alloy identify the features as correlation satellites and give model parameters as follows: charge-transfer energy Δ=1 eV, Coulomb energy U=3 eV, and transfer integral T=1.2 eV. A detailed comparison to the case of c(2×2) Mn/Cu(100) leads to the conclusion that c(2×2) Mn/Ni(110) is a new magnetic surface alloy.