LES analysis was performed using OpenFOAM to investigate the characteristics of vortices in the separated-andreattachment flow between the blades of a sirocco fan. Five models with different blade thicknesses were used. The results showed the followings. (1) As the blade thickness increases, the position of the separation point changes from the leading edge of the blade to the middle of the suction surface. (2) The spectrum of pressure fluctuation between the blades changes along the separated shear layer as vortices merge and reattach when the separation occurs at the leading edge, but almost the same when separation occurs at the middle of the suction surface. (3) The size of the vortex continues to grow at the almost same rate from roll-up to reattachment. Its growing rate is independent of the blade thickness.