The use of microresonators with sharp corners (rectangular and square-shaped) can be limited by severe energy loss at the corners. A 2D numerical study is conducted to investigate and analyze the effect of incorporating fillet (rounding of corners) design at sharp corners of such single-mode optical microresonators. The effect on quality factor, free spectral range, and energy loss for the coupled microresonator-waveguide system in the add-drop configuration for varying values of fillet radii are quantified. It is shown that the selection of an optimum radius of the curvature of the fillet for sharp-cornered microresonators provides a higher quality factor than that of the conventional circular resonators.