The synthesis of thin zeolite nanosheets beneficial for catalytic reactions, adsorption and diffusion involving bulky molecules remains a great challenge. Herein, we report a unique layered zeolitic nanosheet ECNU-57 with a CDO-type structure that was synthesized by employing small-molecular 1,4-bis(N-methylpyrrolidinium) cations as the organic structure-directing agent (OSDA). The ECNU-57 nanosheets are 50 nm thick along the b-axis and have an open hierarchical porosity with 486 m2 g-1 surface area. HRTEM investigation indicates that the nanosheets exhibit a stacking fault structure along the b-axis with the inclusion of the FER structure since the CDO and FER topologies possess very similar building layers. As a solid-acid catalyst, ECNU-57 exhibits promising performances in the reactions of 1,3,5-triisopropylbenzene cracking and Friedel-Crafts acylation, due to its enhanced mass transfer and more accessible active sites to bulky organic molecules.