In this paper, the system parameters of a nonlinear bistable energy harvester excited by Gaussian white noise was investigated. Using Fokker–Planck–Kolmogorov equation, the probability distribution functions of displacement and velocity of the oscillator are obtained. The effect of various system parameters on the probability distributions of displacement and velocity of the oscillator and the mean square of the output voltage are investigated when the time constant of the piezoelectric circuit takes a larger value to achieve maximum voltage gain. The maximum peak values of the joint probability distribution of displacement and velocity of the oscillator decrease with the larger values of noise strength. The effect of parameters of bistable potential function on mean square of output voltage was also investigated. The system equations are numerically solved and mean square value of output voltage is numerically estimated and is seen to be increased as noise intensity increases and decreased as viscous damping increases. The result also shows that better power output can be achieved when the time constant takes larger value. © 2018, King Fahd University of Petroleum & Minerals.