Abstract Mn-substituted hexaaluminate compounds have been investigated as catalysts for high temperature combustion above 1000°C. In this study, changes of crystalline phase and catalytic properties of Sr 1− x Ln x MnAl 11 O 19−α ( Ln = Pr, Nd, Sm, Gd) were investigated. Two kinds of hexaaluminate phases existed as equilibrium phases in the unsubstituted sample, the Ln ions were preferentially soluble in one of these phases. Accompanied with the dissolution, unequilibrium LnAlO 3 phase was sometimes formed for high x samples. The amount of this phase decreases with an increase in temperature and/or ionic radius of Ln . The surface area of the samples generally decreased with increasing extent of Ln substitution. Catalytic activity for methane combustion at low conversion level was improved by the substitution.