Disclosed herein is an organic anti-reflective coating polymer suitable for use in ultrafine pattern formation during fabrication of a semiconductor device. The organic anti-reflective coating polymer has a weight-average molecular weight of about 2,000 to about 100,000 and is represented by Formula 1 below: ##STR00001## wherein R.sub.1 is a C1-C5 linear or branched alkyl group, R.sub.2 and R.sub.3 are each independently hydrogen or methyl, X is halogen, n is a number from 1 to 5, and a, b and c, representing the mole fraction of each monomer, are each independently from about 0.1 to about 0.9. Also disclosed are an organic anti-reflective coating composition comprising the coating polymer and a method for forming a photoresist pattern with the coating composition.