Freestream turbulence effects on laminar separation bubbles in low-Reynolds-number flow over a flat plate are investigated using large eddy simulations. To this end, the framework of the Fourier-series-based synthesized turbulence is introduced to make inflow turbulent fluctuation. The results show that the freestream turbulence accelerates the laminar-turbulent transition and the length of the separation bubble decreases. Consequently, the pressure distributin of the simulations with the freestream turbulence shows closer distributions to an experimental result than the simulation without freestream turbulence. Moreover, a parametric study shows that the length scale of turbulence, as well as the intensity of turbulence, affects the flow reattachment point. This fact may indicate that we have to pay attention to the turbulent length scale in addition to the turbulent intensity on wind tunnel tests.