Recent developments and application of polyisoimide (PII) to high performance materials including synthetic method, high temperature adhesive, photosensitive polymers and rigid-rod molecular composite (RRMC) are described. First, various polyisoimide were prepared by the cyclization of polyamic acids and studied their thermal properties. We found that PIIs have lower glass transition temperatures (Tgs) than that of corresponding polyimides (PIs), and are relatively stable above their glass transition temperature, but easy to convert to corresponding PIs by high thermal treatment. Next these characteristics of PIIs were successfully applied to develop the new high temperature adhesives. PIIs showed strong adhesions to copper foils because of favorable anchoring between PIIs and copper foil due to good flow of PIIs. Then, positive working photo-sensitive polyimide (PSPI) precursors based on PII and 2,3,4-tris[1-oxo-2-diazonaphthoquinone-4-sulfonyloxy]-benzophenone (D4SB) or Nifedipine [l,4-dihydro-2,6- dimethyl-4-(nitrophenyl)-3,5-pyridinedicarboxylic acid dimethylester] (DHP) as a photoreactive compound have been developed. Further, a new amine photogenerator, N-{[(4,5-dimethoxy-2-nitrobenzyl)-oxy]-carbonyl}-2,6-dimethyl piperidine (DNDP) was found to be effective for the isomerization of PII to the corresponding PI. The new negative type PSPI was formulated from PII and DNDP. Finally, an approach to in-situ generated rigid-rod molecular composites (RRMC) from PII and poly(ether sulfone) has been investigated, and transparent composite films were obtained in the PI contents of 2 to 10 wt%.