Electronic Journal of Differential Equations, Vol. 2013 (2013), No. 156, pp. 1-8. Title: Hyers-Ulam stability for Gegenbauer differential equations Author: Soon-Mo Jung (Hongik Univ., Sejong, South Korea) Abstract: Using the power series method, we solve the non-homogeneous Gegenbauer differential equation $$ ( 1 - x^2 )y''(x) + n(n-1)y(x) = \sum_{m=0}^\infty a_m x^m. $$ Also we prove the Hyers-Ulam stability for the Gegenbauer differential equation. Submitted June 19, 2013. Published July 08, 2013. Math Subject Classifications: 39B82, 41A30, 34A30, 34A25, 34A05. Key Words: Gegenbauer differential equation; Hyers-Ulam stability; power series method; second order differential equation.