The aim of this study was to evaluate the efficiency of diammonium phosphate (DAP) and silicate dispersion (SILIC) as a flame retardant system in polylactic acid (PLA)-polycaprolactone (PCL) blends. First polylactic acid and polycaprolactone respectively were mixed in different ratios in order to create the matrix of our polymer. PCL was used to enhance the processability and biodegradability of PLA. Diammonium phosphate was used as a flame retardant additive to create a char protective layer on the polymer’s surface, as it is safe, inexpensive, and more efficient than other phosphorus compounds. Finally silicate dispersion was used as a coating to inhibit pyrolysis gases and to retard thermal degradation and oxidation. The thermal stability and the flame retardant properties were evaluated by thermogravimetric analysis (TGA) and cone calorimeter, respectively. Differential scanning calorimetry was used to study the thermal transition of the samples. Finally, optical microscope (OM) was used to analyse the external char structure, and scanning electron microscopy (SEM) for morphological study of the char. The samples containing DAP and SILIC showed a compact structure and the results from TGA and cone calorimeter suggested that there was a synergistic effect with the addition of the DAP and the coating. The morphological study showed that the addition of DAP along with the coating created a char residue more homogenous and dense than the other composites The cone calorimeter analysis confirms the formation of an intumescent structure for the blends containing DAP and SILIC. The best results were obtained for (PLA-PCL)-30DAP coated, with a final residue corresponding to 64% of the initial sample mass and also a decrease in the peak of heat release (PHRR) rate and total heat release (THR) of 91% and 85% respectively.