Two novel polymers PDPP3T-CN and PDPPTPT-CN containing nitrile-substituted thienyl and phenyl units were designed and synthesized. The influence of nitrile groups on the electronic properties and charge-carrier transport of the polymers was thoroughly investigated and highlighted by comparing with the corresponding non-nitrile substituted polymers. Experimental results showed that the introduction of nitrile groups lowered the HOMO and LUMO energy levels of polymers by about 0.3 eV and 0.2 eV, respectively. Thin film transistor characteristics displayed that both polymers exhibited electron-dominated ambipolar behavior under ambient conditions. The highest electron/hole mobilities were 0.18/0.0083 cm(2) V-1 s(-1) for PDPPTPT-CN and 0.09/0.0017 cm(2) V-1 s(-1) for PDPP3T-CN, one of the highest electron mobilities for DPP-based polymers measured under ambient conditions with bottom-gate/top-contact device configurations.