We performed molecular dynamics simulation of diffusion along symmetric <100> 5 and <111> 7 and one non-symmetric <100> 5 tilt grain boundaries in Al in the presence of Fe impurities. The simulation results are in reasonable agreement with available experimental data. The addition of Fe considerably decreases both Al and Fe diffusivities and increases the activation energy for diffusion. The simulation data indicate that the mechanism of diffusion is different in different grain boundaries. The diffusion along <100> 5 grain boundaries reminds that in liquid alloys.