In this paper, an integrated algorithm for optimization of variogram parameters in 3D stochastic seismic inversion was done using particle swarm optimization (PSO) algorithm. Following variogram modeling, an uncertainty interval for range values were defined, then, the optimized parameters were obtained using PSO algorithm. The inverted acoustic impedance values were produced using the optimized variogram parameters. Proposed method was applied to a synthetic data in two conditions, with and without noise. Results showed optimization convergence and acceptable inverted acoustic impedance values using optimized variogram parameters. Validation of the results were successfully done using two blind wells that were excluded from inversion procedure.