the present invention relates to a process for preparation of polyester resin in the presence of a novel catalyst system comprising an antimony compound and inorganic tin compound . the present invention also relates to a catalyst system for the preparation of polyester comprising an antimony compound and inorganic tin compound which reduces the polymerization time at all stages of polyester synthesis and reduces the generation of degradation product . this invention further relates to polyester resin with improved l color having significant importance in end - use applications .