Spin　injection　across　ferromagnet/organic　semiconductor　system　with　finite　width　of　the　layers　was　studied　theoretically　considering　spin-dependent　conductivity　in　the　organic-semiconductor.　It　was　found　that　the　spin　injection　efficiency　is　directly　dependent　on　the　difference　between　the　conductivity　of　the　up-spin　and　down-spin　polarons　in　the　spin-injected　organic　system.　Furthermore,　the　finite　width　of　the　structure,　interfacial　electrochemical-potential　and　conductivity　mismatch　have　great　influence　on　the　spin　injection　process　across　ferromagnet/organic　semiconductor　interface.　(C)　2008　Elsevier　B.V.　All　rights　reserved.