The present disclosure relates to an organic anti-reflective coating composition and a method for forming photoresist patterns using the same. The anti-reflective coating compositions are useful for preventing reflection of a lower film layer or a substrate of a photoresist film, reducing standing waves caused by light and variations in the thickness of the photoresist itself, and increasing the uniformity of the photoresist patterns. More particularly, the present invention relates to an organic anti-reflective coating composition comprising particular organo-silicon based polymers and a method for forming photoresist patterns using the same. The organic anti-reflective coating composition can prevent excessive absorbency of an anti-reflective film formed therefrom and, thus, minimize the reflectivity of the film so that it can efficiently remove standing waves and increase the uniformity of the photoresist pattern.