Highly dispersed 2D-nanostructured ultrathin black phosphorus nanosheets (BPNs)-integrated Au nanoparticles (AuNPs) hybrids were constructed in situ through a facile and environmentally friendly strategy. No additional reductants, surfactants, or polymer templates were introduced during this green and convenient synthesis process. The resulting AuNPs/BPNs nanohybrids were characterized by UV-vis, Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The content of BPNs plays an essential role in modulating the morphologies and chemical states of AuNPs/BPNs hybrids, which have been investigated systematically and are discussed in detail. As high-density ultrasmall AuNPs are properly stabilized and accommodated without passivation by the surrounding ultrathin BPNs, the resulting AuNPs/BPNs hybrids exhibit excellent catalytic/antibacterial properties and long-term stabilities, benefiting from a possible synergistic enhancement effect between AuNPs and BPNs constructs. This simple, mild and environmentally benign strategy could be generalized to the preparation of other metal- or metal oxide-doped complexes and holds great promise for potential catalytic, bioanalytical and biomedical applications.