Electronic Journal of Differential Equations, Vol. 2023 (2023), No. 21, pp. 1-15. Title: Hyers-Ulam stability of linear quaternion-valued differential equations Authors: Jiaojiao Lv (Guizhou Univ., Guiyang, Guizhou, China) Jinrong Wang (Guizhou Univ., Guiyang, Guizhou, China) Rui Liu (Guizhou Univ., Guiyang, Guizhou, China) Abstract: In this article, we study the Hyers-Ulam stability of the first-order linear quaternion-valued differential equations. We transfer a linear quaternion-valued differential equation into a real differential system. The Hyers-Ulam stability results for the linear quaternion-valued differential equations are obtained according to the equivalent relationship between the vector 2-norm and the quaternion module. Submitted anuary 4, 2023. Published February 27, 2023. Math Subject Classifications: 34D20. Key Words: Hyers-Ulam stability; linear quaternion-valued differential equation.