In this work, an environmentally friendly and energy-saving strategy to decorate Ni-Al layered double hydroxides nanosheets (LDHs@PN) has been utilized to boost their flame retardancy and dispersion in the polymer. This proposed strategy was implemented through noncovalent self-assembly supramolecular aggregate of phytic acid (PA) and 1,4-bis(3-aminoethyl) piperazine (AEP) onto NiAl-LDHs surface in water without any organic solvent. The target product LDHs@PN was investigated by different characterization techniques. It was found that LDHs@PN was successfully fabricated possessing hydrophobic surfaces. In contrast, the surface of LDHs@PN became rough and exhibited a fluffy structure. Meanwhile, Ni, Al, P and N were homogeneously distributed on the surface of LDHs@PN. Significantly, after introducing LDHs@PN into biobased polylactic acid (PLA) via melting-blending, the thermal stability of composites was improved compared to that of pure PLA and LDHs@PN promotes the formation of composite residual carbon. In addition, the PLA/LDHs@PN composite with 20 wt% loadings reached V-0 rating in the UL-94 test and achieved 30.1% limiting oxygen index value, indicating LDHs@PN significantly increased the flame retardant performance of the PLA. The flame retardant mechanism of LDHs@PN in the PLA matrix was analyzed. This facile, low-cost and eco-friendly decorating strategy is promising for industrial production.