<p>In this article, for a degenerate inhomogeneous equation of even order with a fractional derivative in the sense of Caputo, a boundary value problem of the Robin problem type is studied. The solution is constructed in the form of a series of eigenfunctions of a one-dimensional spectral problem for a degenerate equation of even order. The existence and positivity of eigenvalues are shown by reducing the spectral problem to an equivalent integral equation with a symmetric kernel. Also, when constructing the posed problem, a boundary value problem for a one-dimensional fractional order equation was studied. Depending on the sign of the constant coefficient of the equation <i>q</i>, the necessary estimates for the solution were obtained. Sufficient conditions for the convergence of the series, which is a solution to the Robin problem, and the series obtained by differentiation are found. The uniqueness of the solution is demonstrated by the spectral method.</p>