Disubstituted pendant-functionalized block copolymer consisting of insulating polynorbornene and conductive polyacetylene segments was synthesized by tandem metathesis polymerization, and displayed high dielectric constant of 30 and low dielectric loss of about 0.04, while behaved bad film-forming property, which could be improved by incorporating polycyclooctene into polynorbomene backbone. The generated flexible block copolymer with well-defined nanostructure exhibited a relatively high dielectric constant of 23, very low dielectric loss of below 0.0035, and high stored and released energy densities up to 4.52 and 4.02 J cm(-3) at the electric field of 165 MV m(-1),respectively, accompanied with the charge-discharge efficiency of 90%. The enhanced dielectric and energy storage capability were attributed to high permanent dipole moment and the interfacial polarization derived from the unique nanomorphology of block copolymer.