An organo-inorganic composite material PANI-APP based on conjugated polyaniline (PANI) and ammonium polyphosphate (APP) was prepared by performing in situ polymerization of aniline with ammonium persulfate in the presence of APP, and then it was doped by P-toluene sulfonic acid (PTSA). PANI(PTSA)-APP was possessed of flame retardancy and electrical conductivity and it was introduced into high density polyethylene for preparing PE/PANI(PTSA)-APP composites. The structural and morphological properties of PANI(PTSA)-APP were analyzed by Fourier transform infrared spectroscopy, X-ray diffraction (XRD) and other analyses. The results showed that PANI doped with PTSA was prepared. The electrical conductivity and flame retardancy of PE/PANI(PTSA)-APP composites were investigated by measuring the electrical resistance and scanning electron microscope, photomicrography, limiting oxygen index (LOI), thermal gravity (TG) and XRD, respectively. Experimental results showed that the LOI of composite reached to 29.2% and the volume resistivity dropped to 6.80 x 10(8) Omega cm(-1) when the amount of PANI(PTSA)-APP was 30%. The thermal degradation mechanism of PANI(PTSA)-APP was explored and we found out that PANI(PTSA) coupled with APP had a positive synergistic effect on the flame retardancy.