New high-temperature adhesives based on polyisoimide (PII) have been developed. PIIs were prepared by the ring-opening polyaddition of 4,4’-hexafluoroisopropylidenebis(phthalic anhydride) and 4,4’-[hexafluoroisopropylidenebis( p-phenyleneoxy)] dianiline or 4,4’-[isopropylidenebis(p-phenyleneoxy)]dianiline, followed by treatment with trifluoroacetic anhydride-triethylamine in N-methyl-2-pyrrolidone. Compared to those of polyimides (PIs), the glass transition temperatures (T-g) of PIIs were lower and the elasticities were greatly reduced above their T-g. Furthermore, PIIs showed stronger adhesion to copper foils. The interfacial surface morphologies of PII films after adhesion testing were investigated by scanning electron microscopy and energy-dispersive X-ray analysis. The results suggested that the good adhesion bond strength was produced by favourable anchoring between PII and copper foil due to a good flow of PII.