The aim of this work is to develop an environmentally friendly, safe, and simple route for realizing efficient preparation of aspirin. Here, inspired by enzyme synthesis in vivo, we have realized the aspirin synthesis by sub-nanoconfined esterification with directional flow and ∼100% conversion in an unprecedented reaction time of <6.36 s at 23°C. Such flow esterification reaction is catalyzed by thermally transformed graphene oxide (GO) membranes with tailored physicochemical properties, which can be obtained simply through a mild annealing method. A possible mechanism was revealed by density functional theory (DFT) calculation, indicating that the synergistic effect of spatial confinement and surface electronic structure can significantly improve the catalytic performance. Confined in 2D sub-nano space created by GO-based laminar flow-reactors, the present strategy provides a new route to achieve rapid flow synthesis of aspirin with complete conversion. This article is protected by copyright. All rights reserved.