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Epoxy has become an integral insulating material for electric and electronic devices due to its excellent mechanical and electrical performance. However, tracking failure on the epoxy surface is an unavoidable phenomenon in the increasing application. Based on the viewpoint of material modification, the properties of composite materials can be changed by the nano-particles. Whether the tracking resistance of epoxy nanocomposites can be improved needs better understanding for the reliable application. In this paper, nano-TiO2 particles were mixed into pure epoxy to obtain the epoxy/TiO2 nanocomposites with the weight ratios of 1, 3, 5, 7 wt%, respectively. Tracking experiments were carried out to investigate the effects of nano-TiO2 concentration on the tracking failure by applying dc voltage. The dc resistance to tracking failure, tracking process and discharge current were measured in relation with the concentration of TiO2 and the applied voltage. Obtained results indicate that with the concentration from 0 to 5 wt%, the number of drops to tracking failure shows the increasing tendency and the erosion depth shows the decreasing tendency. But they show the opposite varying tendency with the concentration from 5 to 7 wt%. Additionally, the fractal dimension method was applied to quantitatively reveal the nonlinear characteristics of both scintillation discharge distribution and tracking pattern for the purpose of identifying the concentration effects on the process of tracking failure. The recurrent plot technique was employed to reveal the nonlinear characteristics of discharge currents, which can reflect the underlying mechanism in the tracking failure affected by the nano-TiO2 particles. Therefore, the experimental results suggest that the tracking resistance of epoxy can be improved by nano-TiO2 particles, especially mixed with the concentration of 5 wt%.