The presence of DFIG (Doubly Fed Induction Generator) affecting the stability of the inter-area interconnected power system due to the lagging response of DFIG under undesirable conditions like faults. This paper addresses a Second-order Sliding Mode controller for DFIG to damp inter-area frequency oscillations of the interconnected power system. The proposed heuristic controller is a sliding mode controller of second-order type and works based on the reactive power capability of DFIG. This novel controller is not affected by system modeling uncertainties and unwanted parameter variations. The proposed controller is designed and implemented on 3-bus interconnected system in MATLAB/Simulink environment and the results obtained compared with the conventional controller under different fault conditions to show the effectiveness. Results demonstrated that the sliding mode controller effectively damping inter-area oscillations compared with a conventional controller.