The　recent　growth　in　network　usage　has　motivated　the　creation　of　new　malicious　code　for　various　purposes,　including　economic　ones.　Today＇s　signature-based　anti-viruses　are　very　accurate,　but　cannot　detect　new　malicious　code.　Recently,　classification　algorithms　were　employed　successfully　for　the　detection　of　unknown　malicious　code.　However,　most　of　the　studies　use　byte　sequence　n-gram　representation　of　the　binary　code　of　the　executable　files　on　windows.　We　propose　the　use　of　Dalvik　Operation　Code　on　Android,　generated　by　disassembling　the　application.　We　then　use　n-gram　of　the　operation　code　as　features　for　the　classification　process.　We　present　a　full　methodology　for　the　detection　of　unknown　malicious　code,　based　on　text　categorization　concepts.　The　experiment　results　show　that　the　method　results　are　in　a　high　accuracy　rate.