A series of aromatic copolyimides was success fully synthesized from the commercial pyromellitic dianhy dride (PMDA) with a commercial diamine p-phenyldiamine (PDA) and a diamine 4,4’-methylenebis-(2-tert-butylaniline)(MBTBA) specially designed by the authors.The copoly imides were characterized by Infra-red (IR),Nuclear Magnetic Resonance (NMR),Gel Permeation Chromato graphy (GPC),Ultraviolet Visual (UV-Vis),Thermogra vimetic Analysis (TGA) and Dynamic Mechanical Analysis (DMA).The copolyimide was precipitated in m-cresol in the polymerization process when the molar ratio of MBTBA and PDA was lower than 6/4.The number-average molecular weight of the soluble copolyimides measured by GPC was larger than 4.0 x 104,and the polydispersity index was higher than 1.5.Only one glass transition temperature of these copolyimdies was detected around 360℃ by DMA.The copolyimides did not show appreciable decomposition up to 500℃ under N2,and the thermal stability of the copolyimide increased a little with the introduction of PDA into the polyimide main chain.