Consider a Cerenkov laser, using for the slow‐wave structure a dielectric waveguide whose substrate consists in a nonlinear dielectric presenting the self‐focusing effect. The characteristics of the Cerenkov laser specified in the foregoing are investigated theoretically for the two‐dimensional model which takes into account the field distribution in the transverse direction. First, the dispersion relations are considered for the electromagnetic wave modes (TM waves) propagated along a two‐dimensional nonlinear dielectric waveguide. Then the dispersion relations are discussed for the coupled electromagnetic fields in the Cerenkov laser using the nonlinear dielectric waveguide. Finally, the spatial growth rate of the growing wave obtained from the dispersion relation for the coupled fields derived in the foregoing is investigated numerically in detail. From the forementioned discussion, it is found that the spatial growth rate for the Cerenkov laser treated in this paper is improved compared to the Cerenkov laser for which the slow‐wave structure is composed of linear dielectrics only.