PEGDA/PETEDA dendrimer composite membranes was prepared by UV photopolymerizing of poly ethyleneglycol diacrylate (PEGDA) containing 5∼15 wt% pentaerythrityl tetraethylenediamine (PETEDA) dendrimer. The preparedcomposite membrane was characterized by FT-IR, ¹H-NMR and DSC. The glass transition temperature (T_g) of PEGDA/PETEDA dendrimer composite decreased with the increment of PETEDA dendrimer content. The CO₂ separation propertiesover CH₄ were investigated by changing the PETEDA dendrimer content and pressure. The composite membrane containing10 wt% PETEDA dendrimer exhibited on excellent CO₂/CH₄ ideal selectivity of 31.8 and a CO₂ permeability of 162.2barrer.