Heat seal properties and mechanism of heat sealable polypropylene (PP) film were studied. The PP film was compounded PP homo-polymer (homo-PP) with poly(ethylene-co-propylene) (co-PP). Ethylene component of co-PP was less than 5%. Dry blended homo-PP with co-PP was compounded by twin-screw extruder and directly casted into film. After processing film heat seal tests were carried out. Heat seal strength of the PP film compounded 10wt% co-PP components was higher than the other PP film at 150 degrees C of heat seal temperature. Heat sealed region for the PP film were evaluated in wide angle x-ray diffraction (WAXD), small angle x-ray scattering (SAXS) and differential scanning calorimetry (DSC) measurement. For the PP film compounded 10wt% co-PP components, crystallization was suppressed in film processing and however promoted effectively in heat seal process at 150 degrees C of heat seal temperature by WAXD, SAXS and DSC studies. A few compounded co-PP components, 3wt% could not suppress crystallization in film processing and crystallization did not promote in heat seal process. Most compounded co-PP components, 20wt% suppressed crystallization in film processing and also in heat seal process. Compounded co-PP components worked effectively at 10wt% for improving heat seal properties of PP homo-PP film. The PP film compounded 10wt% co-PP components showed high crystallization rate in isothermal crystallization study in DSC.