Disclosed is an organic antireflective film composition which includes a monomer containing two or more thiol groups and a monomer containing two or more vinyl groups, as crosslinking agents. When the organic antireflective film composition is used, an antireflective film formed from the composition can be rapidly etched in an ultrafine pattern forming process, and the curing rate can be increased, while the etching rate is increased, without using an acid generator and a curing agent or by using the agents only in small amounts.