Axial segregation of a bidisperse mixture of particles in a long rotating drum is studied using the discrete element method. Simulation results show that particle interaction is responsible for axial segregation,the patterns of which are influenced by the end wall effect. Axial segregation patterns transform under competing influences of the end walls and the particle interaction forces. The two influential factors vary with various rotational speeds and end wall friction levels. The result is the transition of different axial segregation patterns: two large-particle bands at both ends, two small-particle bands at both ends, or a random segregation pattern where either a large-particle band or small-particle band may appear at either end. Axial segregation of a bidisperse mixture of particles in a long rotating drum is studied using the discrete element method. The two influential factors vary with various rotational speeds and end wall friction levels. The result is the transition of different axial segregation patterns: two large-particle bands at both ends, two small- particle bands at both ends, or a random segregation pattern where either a large-particle band or small-particle band may appear at either end.