Abstract
In this paper, we provide new generalizations for the Gronwall's inequality in terms of a psi-fractional operator. The new forms of Gronwall's inequality are obtained within a general platform that includes several existing results as particular cases. To apply our results and examine their validity, we prove the existence and uniqueness of solutions for psi-fractional initial value problem. Further, the Ulam-Hyers stability of solutions for psi-fractional differential equations is discussed. For the sake of illustrating the proposed results, we give some particular examples.