Carbon molecular sieve is introduced as flexible supercapacitor electrode for the first time. The carbon molecular sieve electrode generates a specific capacitance of 108.0 F.g(-1) and demonstrates an excellent stability with 98.5% preservation of its initial capacitance after 10,000 charging-discharging cycles. To further enhance the electrochemical performance, a flexible 3-D structured composite electrode is synthesized via an electrochemical polymerization method by depositing poly 3,4-ethylenedioxythiophene film on the carbon molecular sieve surface, denoted as carbon molecular sieve@poly 3,4-ethylenedioxythiophene. The specific capacitance of the composite electrode is up to 126.0 F.g(-1), higher than both poly 3,4-ethylenedioxythiophene (115.7 F.g(-1)) and carbon molecular sieve (108.0 F.g(-1)). Moreover, the flexible composite electrode preserves 96.0% of its initial capacitance after 10,000 charging-discharging cycles at 1.00 A.g(-1). The superior performance of the composite electrode is attributed to the combined merits of the superior conductivity and excellent cycle stability of the carbon molecular sieve and 3-D porous network configuration of the poly 3,4-ethylenedioxythiophene.