Prevention of slipping accidents requires provision of adequate friction through the use of suitable combinations of footwear and underfoot surfaces. Shoe sole tread groove is one of the important factors on friction coefficient during walking.To measure the effect of different shoe sole tread groove depths and different surfaces on the required quotient of friction (Q), heel strike velocity and occurrence time of ground reaction forces (GRF) in stance phase during walking on slippery and dry surfaces.In this semi-experimental study, 22 healthy men were studied under different conditions. The studied independent variables were shoe groove depths (included 1, 2.5 and 5 mm) and type of walking surface (dry and slippery). Biomechanical gait analysis was carried out with 396 single steps. Data were collected by motion analysis system and two force platform.The occurrence time of GRF was significantly faster on dry surface than slippery surface (p<0.01). Q was significantly lower on slippery surface and with groove depths of 1 and 2.5 mm. The highest value of Q was observed with the deepest groove depth of 5 mm. Heel strike velocity did not differ significantly in the 6 conditions tested.Tread groove depth is a significant factor affecting the Q at the shoes-surface interface on dry and slippery floors. It seems that deeper groove is more appropriate for maintaining the stability during walking. The walking surface affects the occurrence time of GRF; the force components occur sooner on the dry than slippery surface.