A magnetoresistance effect element and a Heusler alloy in which a state change due to annealing does not easily occur. The element includes a first ferromagnetic layer, a second ferromagnetic layer, and a non-magnetic layer positioned between the first ferromagnetic layer and the second ferromagnetic layer, in which at least one of the first ferromagnetic layer and the second ferromagnetic layer is a Heusler alloy in which a portion of elements of an alloy represented by Co2FeαZβ is substituted with a substitution element, in which Z is one or more elements selected from the group consisting of Al, Si, Ga, Ge, and Sn, α and β satisfy 2.3≤α+β, α