Photoresist polymers and photoresist compositions are disclosed. A photoresist polymer represented by Formula 1 and a photoresist composition containing the same have excellent etching resistance, thermal resistance and adhesive property, and high affinity to an developing solution, thereby improving LER (line edge roughness). wherein X1, X2, X3, R1, R2, R3, R4, R5, m, n, o, a, b, c, d and e are as defined in the description.