The　influence　of　grain　size　on　the　corrosion　behavior　of　pure　aluminum　and　the　defect　density　and　diffusion　coefficient　of　surface　passive　films　were　investigated　using　electron　backscatter　diffraction　(EBSD)　and　electrochemical　testing　techniques,　based　on　the　point　defect　model　(PDM).　Samples　with　three　different　grain　sizes　(23　+/-　11,　134　+/-　52,　and　462　+/-　203　mu　m)　were　obtained　by　annealing　at　different　temperatures　and　times.　The　polarization　curves　and　electrochemical　impedance　spectroscopy　results　for　the　pure　aluminum　in　the　3.5%　NaCl　solution　showed　that　with　decreasing　grain　size,　the　corrosion　current　(icorr)　decreased　monotonously,　giving　rise　to　a　noble　corrosion　potential　and　a　large　polarization　resistance.　The　Motte-Schottky　results　showed　that　the　passive　films　that　formed　on　pure　aluminum　with　fine　grains　of　23　+/-　11　mu　m　had　a　low　density　(3.82　x　1020　cm-3)　of　point　defects,　such　as　oxygen　vacancies　and/or　metal　interstitials,　and　a　small　diffusion　coefficient　(1.94　x　10-17　cm2/s).　The　influence　of　grain　size　on　corrosion　resistance　was　discussed.　This　work　demonstrated　that　grain　refinement　could　be　an　effective　approach　to　achieving　high　corrosion　resistance　of　passive　metals.