A　bio-polyelectrolyte　(PC)　was　synthesized　by　reacting　phytic　acid　(PA)　with　casein　(CS),　and　used　as　the　shell　materials　to　microencapsulate　ammonium　polyphosphate　(APP).　The　obtained　core-shell　structured　flame　retardant　(PC@APP)　was　incorporated　into　polylactic　acid　(PLA).　The　dispersion　of　PC@APP　was　greatly　improved.　As　a　result,　the　elongation　at　break　and　notched　impact　strength　were　improved　from　6.9%　and　3.5　KJ/m(2)　of　neat　PLA　sample　to　14.4%　and　4.7　KJ/m(2)　of　PLA　samples　containing　5%PC@APP.　Moreover,　the　fire　resistance　of　PLA/5%PC@APP　composites　was　also　enhanced.　The　limiting　oxygen　index　(LOI)　value　was　increased　from　19.6%　to　28.3%;　the　vertical　burning　(UL-94)　rating　was　upgraded　from　no　rating　to　V-0;　and　the　peak　heat　release　rate　value　was　decreased　from　935.8　kW/m(2)　to　747.9　kW/m(2).　It　is　suggested　that　the　well-dispersed　PC@APP　alters　the　degradation　routine　of　PLA　matrix,　leading　to　the　rapid　formation　of　physical　barriers.