A photoresist composition for preventing exposing failures and a method of forming a pattern using the same are disclosed. The photoresist composition preferably comprises about 0.1% to about 0.5% by weight of a photo acid generator, and about 2% to about 10% by weight of a polymer resin, the PAG including a monophenyl sulfonium compound, a triphenyl sulfonium compound or a mixture thereof. The footing phenomenon and the top loss of a pattern are sufficiently prevented.