Previous studies on low Reynolds number quasi-2D flow around airfoils were mostly two-dimensional, with issues for stalling behavior at higher angles of attack (AOAs). In the present work, a computational study was conducted to investigate the unsteady quasi-2D flow around a streamlined NASA low-speed GA(W)-1 airfoil and a corrugated dragonfly airfoil at the Reynolds numbers of 68,000 and 55,000 with both 2D and 3D simulations. These simulations were carried out by solving the unsteady 2D and 3D Navier-Stokes equations to predict the behavior of the unsteady flow structures around the airfoils at different AOAs. Extensive comparisons were made between the numerical results and wind-tunnel experimental results for the same configurations. It was found that the 2D and 3D simulations differ significantly at relatively high AOAs, and that the 3D computational results agree much better with the experimental data. It is believed that unsteady vortex-dominated flow at high angle of attack is strongly three-dimensional. As a result, the 2D simulations are not adequate in resolving the fundamental flow physics, and 3D simulations are necessary to correctly predict the flow behavior at such conditions.