Phase properties of gradientABcopolymer melts which consist of chains with the specified chemical distribution ofAandBmonomers have been studied within the Landau-Ginzburg model. All the melts with the linear distribution of the monomers exhibit only a direct continuous phase transition from disordered to the lamellar phase. The hexagonal, body-centered-cubic, double-gyroid(G) and lamellar ordered structures have been found in the melts with the monotonic but nonlinear distribution of the monomers. The G structure has been also found in the gradient copolymer melts with the distribution function of monomers similar to theA−B−Atriblock copolymers. ©2000 American Institute of Physics.