A polymer including a monomer represented by the following Formula and a photoresist composition including the same are disclosed. The polymer and photoresist composition can improve the resolution and the process margin due to the low activation energy of the deprotection reaction of the alcohol ester group including saturated cyclic hydrocarbyl group, and also can produce fine photoresist patterns because they have a stable PEB(Post Exposure Baking) temperature sensitivity, and further, can improve the focus depth margin and the line edge roughness of the resist layer. In the above Formula, R* is a hydrogen or methyl group, R1 is saturated hydrocarbyl group of 1 to 5 carbon atoms, R is mono-cyclic or multi-cyclic homo or hetero saturated hydrocarbyl group of 3 to 50 carbon atoms, and n is an integer of at least 2.