A type of soluble and thermally stable ladder-type poly(p-phenylene) (LPF) with fluorene units in polymer backbone has been synthesized by Suzuki coupling and Friedel-Crafts ring-closing reaction. The full characterization of structures and properties as well as the performances of electroluminescence devices of the new ladder polymers are presented. LPFs show the well-defined structures, high molecular weights, excellent thermal stability, and good solubility in common organic solvents. The high-efficiency emission and absence of low-energy emission band in photoluminescence spectra are observed from LPFs both in the solution and in the solid film. Furthermore, the single layer light-emitting device using LPFs as the active layer shows very stable blue-green emission with maximum luminescence of 5400 cd/m(2) and maximum luminance efficiency of 0.66 cd/A. The extraordinary low concentration of keto defects in LPFs may be corresponding to the improvement in optical and device properties. The attractive properties exhibited by new ladder-type poly(p-phenylene)s establish them as good candidates for active layers in light-emitting devices.