  This paper deals with the existence and uniqueness of solutions for a
nonlinear boundary value problem involving a sequential $\psi$-Hilfer
fractional integro-differential equations with nonlocal boundary conditions.
The existence and uniqueness of solutions are established for the considered
problem by using the Banach contraction principle, Sadovski's fixed point
theorem, and Krasnoselskii-Schaefer fixed point theorem due to Burton and Kirk.
In addition, the Ulam-Hyers stability of solutions is discussed. Finally, the
obtained results are illustrated by examples.
