We have developed a 3-D numerical model of obliquely subducting slab and mantle flow above. Using this model, we explore the effects of oblique subduction on the small-scale convection within the mantle wedge. We find that the spatial pattern and time dependent characteristics of oblique subduction are similar to those of non-oblique cases whose subduction speed is the same as the subduction velocity component normal to the strike of subducting slab. This also implies that the axes of rolls of small-scale convection are nearly normal to the plate boundary, assuming that the plate boundary represents the strike of subducting plate. Only when the back-arc lithosphere overlying the small-scale convection moves along the strike of subduction, a significant change of the orientation of roll axes is observed.