Starch containing polypropylene (SCP) semibiocomposites were prepared by melted blend method. Microencapsulated ammonium polyphosphate (MCAPP) was added to the SCP not only to improve its flame retardant properties but also to restrain the reaction between ammonium polyphosphate (APP) and starch during processing. The flame retardant properties of SCP have been investigated by limited oxygen index (LOI), UL-94 test, and cone calorimeter test. The results of cone calorimeter show that the peak of heat release rate and total heat release of SCP decreases substantially compared with that of pure PP. The thermal degradation and gas products of PP/starch/MCAPP systems were monitored by thermogravimetric analysis (TGA) and thermogravimetric analysis-infrared spectrometry (TG-IR). Scanning electron micrograph (SEM) and X-ray photoelectron spectroscopy (XPS) measurements were utilized to investigate the chemical structure, as well as the surface morphology of the residual char.