In this article, the Adomian Decomposition Method (ADM) is used to study the harmonic oscillators [6]. The obtained discrete solutions using ADM are compared with the Runge-Kutta (RK) method, Single-term Haar wavelet series (STHW) and ODE45 solutions of the harmonic oscillators and are found to be very accurate. Solution and Error graphs for discrete and exact solutions are presented in a graphical form to show efficiency of this method. This ADM can be easily implemented in a digital computer and the solution can be obtained for any length of time.