Large eddy simulations (LES) for mixing process in a stirred tank of 0.476 m diameter with dual Rushton turbines are reported. The computational fluid dynamics (CFD) package FLUENT6.1 was used. The turbulent flow field and mixing time were calculated by using LES with Smagorinsky-Lilly subgrid scale model. The impeller was modeled using the sliding mesh technique. LES results show a better agreement with the mixing experiments than those with standard k-ε model based on Reynolds-averaged Navier-Stokes (RANS) approach. The local curves of tracer response predicted by LES are also in good agreement with the experimental data. The results confirm that LES is a reliable approach for investigations of the unsteady and quasi-periodic behavior of the turbulent flow in stirred tanks.