Abstract: A resin with low polydispersity index and a process for preparing the same. The process includes polymerizing at least one monomer with an initiator and a chain transfer reagent, wherein the monomer is an acrylate monomer having at least one ethylenically unsaturated bonds or norbornene derivatives. Furthermore, a photoresist composition containing the resin composition according to the present invention can increase pattern resolution in lithography process.