Hydrotalcite-like anionic clays or layered double hydroxides with dodecylbenzenesulfonate anions (NiFe, NiAl, and NiCr LDH-SDS, where SDS denotes sodium dodecyl sulfate) were prepared by the coprecipitation method. Hexaphenoxycyclotriphosphazene (HPCP) is an effective cyclophosphazene flame retardant. The HPCP molecule contains a cyclic backbone consisting of alternating phosphorus and nitrogen atoms. LDH-SDS and HPCP were first used to prepare poly(lactic acid) (PLA) composites. One goal of this work was to compare the thermal stability and flame retardancy of PLA/HPCP/LDH-SDS composites. The structures and properties of LDH-SDS materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). Thermal analysis and char residue analysis of PLA/HPCP/LDH-SDS composites suggested that NiFe, NiAl, and NiCr LDH-SDS materials play different roles in improving the thermal stability and flame retardancy of PLA composites. The effective mechanism of LDH-SDS and HPCP in PLA composites is also hypothesized in this work.