Studies have been conducted to explore thermal imidization of polyamic acid. Aromatic polyimides are well recognized as high temperature linear polymers, and polyimide are used as structural materials, fibers, and adhesive. Two different kinds of polyimide were prepared by theimidization of polyamic acid which were synthesized from 2,2-bis[4-(4-aminophenoxy)phenyl]- hexafluoropropane, 2,2-bis [4-(4-aminophenxy)phenyl] - hexamethylpropane and caprolactam and pyromelliti dianhydride under N-Methly-pyrrolidinone solvent. Polyamic acids were converted to polyimides containing imide bond by thermal imidization. The weight 50% loss temperatures of polyimide by TGA thermogram were recorded in the range of 700 ~ 720$^{circ}$C in nitrogen gas. According, as a results, we conclued polyamic acid were cycliation after H2O molecule separationed, and this polyimide film could be used for Printed Circuit Boand.