In this paper, we consider the additive-cubic-quartic functional equation 11 [ f ( x + 2 y ) + f ( x − 2 y ) ] = 44 [ f ( x + y ) + f ( x − y ) ] + 12 f ( 3 y ) − 48 f ( 2 y ) + 60 f ( y ) − 66 f ( x ) and prove the generalized Hyers-Ulam stability of the additive-cubic-quartic functional equation in Banach spaces.