Electronic Journal of Differential Equations, Vol. 2008(2008), No. 72, pp. 1-12. Title: Solvability of characteristic boundary-value problems for nonlinear equations with iterated wave operator in the principal part Authors: Sergo Kharibegashvili (A. Razmadze Math. Institute, Georgia) Bidzina Midodashvili (A. Razmadze Math. Institute, Georgia) Abstract: A characteristic boundary-value problem for a hyperbolic equation with power nonlinearity and iterated wave operator in the principal part is considered in a conical domain. Depending on the exponent of nonlinearity and spatial dimensionality of the equation, the existence and uniqueness of the solution of a boundary-value problem is established. The non-solvability of this problem is also considered here. Submitted February 18, 2008. Published May 15, 2008. Math Subject Classifications: 35L05, 35L35, 35L75. Key Words: Characteristic boundary-value problem; hyperbolic equations; wave operator; power nonlinearity; nonexistence.