This　paper　proposes　an　approach　for　automated　composition　of　Web　services　using　the　And/Or　graph　and　designs　a　corresponding　layered　architecture.　The　composition　approach　which　decomposes　tasks　into　smaller　And,　Or　subtasks　in　And/Or　graph　bases　on　the　similarity　algorithm　to　find　out　optimized　solution　graph.　Additionally,　we　embed　the　Sequence-And　node　to　support　the　transition　from　the　And/Or　solution　graph　to　executable　workflow,　and　Interface　node　to　provide　user　preferences　and　correctness　inspection　during　the　composition　execution.　The　architecture　corresponding　to　the　composition　approach　above　consists　of　four　layers　including　the　Knowledge　Ontology,　Task　Template,　Mediator,　and　Web　Service　from　up　to　bottom　in　the　order.　A　motivation　example　throughout　this　paper　provides　a　preliminary　experimental　illustration　which　clearly　shows　the　benefits　of　our　approach.　©　2008　IEEE.