Among the rising 2D soft materials, conjugated polymer nanosheets are one of the most promising and new classes of polymeric materials, which are rarely developed because of the challenge in controlling the dimensionality and lack of synthetic strategies. In this study, one kind of sulfur-enriched conjugated polymer nanosheet (2DP-S) with a high aspect ratio of up to approximate to 400 is successfully synthesized. On the basis of structural characterization, as-prepared 2DP-S possesses the chemical identity of cruciform-fused polymeric backbone consisting of quinoidal polythiophene and poly(p-phenylenevinylene) along horizontal and vertical directions, respectively, by sharing two alternating single-double carbon-carbon bonds in each repeat unit. The unique structural conformation of 2DP-S renders carrier mobilities of up to 0.1 +/- 0.05 cm(2) V-1 s(-1), a figure inferred from Terahertz time domain spectroscopy. Moreover, upon thermal treatment, 2DP-S is readily converted into N/S dual-doped porous carbon nanosheets (2DPCs) under ammonia atmosphere, whose N/S ratio can be rationally controlled by adjusting the activation time. The catalytic performance of the oxygen reduction reaction of as-prepared 2DPCs is well tunable by the rationally controlled N/S contents. These results offer a new pathway for exploring heteroatom-doped porous carbons applicable for energy conversion and storage.