Disclosed are a light absorbent agent polymer for organic anti-reflective coating which can prevent diffused light reflection of bottom film layer or substrate and reduce standing waves caused by a variation of thickness of the photoresist itself, thereby, increasing uniformity of the photoresist pattern, in a process for forming ultra-fine patterns of photoresist for photolithography by using 193 nm ArF among processes for manufacturing semiconductor devices, and its preparation method. Also, the present invention discloses an organic anti-reflective coating composition comprising a light absorbent agent polymer for the organic anti-reflective coating and a pattern formation process using the coating composition.