Unsatisfied dielectric property and insufficient thermal stability are major obstacles for the commercialization of polyimide resins in the future ultralarge scale integration (ULSI) or radar-wave-transparent composite applications. The incorporation of ortho-hydroxy diamine into a common phenylethynyl terminated oligoimides, aiming to subsequently form additional rigid benzoxazole units by the thermal rearrangement (TR), were prepared. The effects of TR-able codiamine on the processing ability of oligoimides, molecular packing and properties, including thermal stability, dielectric property and bonding ability to reinforcing fibers, for the resulting poly(imide-co-benzoxazole) (PI-co-PBOs) resins have been examined in detail. These thermally rearranged PI-co-PBO resins exhibit reduced dielectric constants of 2.56-3.4 at f = 0.1 GHz, lower than the cured PI with a dielectric constant of 3.55. Meanwhile, the 5 wt% weight loss temperature (T-d5) of the resultant resins increases from 455 degrees C for the cured PI to 491 degrees C for the PI-co-PBO-60 containing 60 mol% benzoxazole unit, and correspondingly, the tensile modulus of PI-co-PBO-60 reaches 2.47 GPa, which is 76% higher than that of the cured PI. These resultant PI-co-PBOs exhibit the combined excellent properties, indicating them a great potentials as the new low-dielectric constant polymer resins in microelectronic industries or advanced composites.