A?single?degree?of?freedom dry friction oscillator with small damping driven by periodic excitation is investigated in this paper. The Melnikov method is used to obtain the parameter region of the horseshoe type chaos. By means of numerical method, the phase diagram and Poincare section diagram of the system with different parameters are given. The Lyapunov exponent of the system is also calculated. Numerical results verify the analytical results, indicating that the system undergoes periodic doubling and turns into chaos.