Abstract: Lanthanum phenylphosphinate (LaP) was synthesized by a simple method and then introduced into polylactide (PLA) to prepare a series of PLA/LaP composites. The thermal stability, flame retardancy and combustion properties of the resulting composites were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), vertical burning experiments and microscale combustion calorimeter (MCC). The results indicated that the incorporation of LaP could enhance the flame retardancy of PLA, and the composites achieved an LOI of 24.8 vol% and a V-2 classification in the UL 94 vertical burning test when 30 wt% of LaP was added. TGA measurement confirmed that LaP could effectively enhance degradation temperature and char residue of the composites. MCC analysis indicated that a high LaP loading could significantly decrease the peak heat release rate and total heat release of the composites, thus reducing the fire hazard of the composites.