A biodegradable two-dimensional (2D) delivery platform based on loading black phosphorus nanosheets (BPs) with Cas9 ribonucleoprotein engineered with three nuclear localization signals (NLSs) at C terminus (Cas9N3) is successfully established. The Cas9N3-BPs enter cells effectively via membrane penetration and endocytosis pathways, followed by a BPs biodegradation-associated endosomal escape and cytosolic releases of the loaded Cas9N3 complexes. The Cas9N3-BPs thus provide efficient genome editing and gene silencing in vitro and in vivo at a relatively low dose as compared with other nanoparticle-based delivery platforms. This biodegradable 2D delivery platform offers a versatile cytosolic delivery approach for CRISPR/Cas9 ribonucleoprotein and other bioactive macromolecules for biomedical applications.