Harvesting energy from the ambient vibration continually attracts significant interest, especially in applications where conventional energy sources are not available. In a conventional mass-spring-damper energy harvester, the harvested energy is limited significantly due to the confined motion of the proof mass. In this study, a nonlinear damping system is proposed, in which damping increases as the proof mass approaches the displacement limits. This way, the average velocity of the proof mass in one cycle increases, resulting in higher generator efficiency. The efficiency of the system was analyzed and compared with a linear damping system. For this purpose, one linear damping and two similar nonlinear damping systems were modeled and solved in MATLAB environment numerically. The results show that the normalized harvested power can be increased 15% by using an optimized nonlinear damping system compared to an optimized linear system, for an ambient vibration amplitude and frequency of 0.09 m and 50 rad/sec, respectively. In addition, it is found that the normalized harvested power over a range of ambient vibration amplitude (0 – 0.09 m) can be increased 93% with nonlinear damping. It is concluded that nonlinear damping system can be an effective method that improves the efficiency of future energy harvesting systems.