In this paper, we obtain the general solution of a generalized cubic functional equation, the Hyers-Ulam-Rassias stability, and the stability by using the alternative fixed point for a generalized cubic functional equation $$4f(sum_{j=1}^{n-1};x_j;+;mx_n);+;4f(sum_{j=1}^{n-1};x_j+mx_n;x_j;-;mx_n};+;m^2sum_{j=1}^{n-1};(f(2x_j);=;8f(sum_{j=1}^{n-1};x_j);+;4m^2{sum_{j=1}^{n-1}};(f(x_j+x_n);+;f(x_j-x_n))$$ for a positive integer $m;{geq};1$.