The photoresist monomer including an oxime group, a polymer thereof and a photoresist composition containing the same are disclosed. The photoresist monomer is represented by following Formula. In Formula, R* is independently a hydrogen or a methyl group, and R is a substituted or unsubstituted C1˜C25 alkyl group with or without an ether group, or a substituted or unsubstituted C4˜C25 hydrocarbon group including an aryl group, a heteroaryl group, a cycloalkyl group or a multicycloalkyl group with or without an ether group, a ketone group or a sulfur.