An　ultra-thin　InAs　layer　with　a　thickness　of　1　monolayer　(ML)　has　been　inserted　at　the　direct　(AlGaAs-on-GaAs)　and　inverted　(GaAs-on-AlGaAs)　interfaces　in　(001)-grown　GaAs/AlGaAs　quantum　wells　(QWs)　with　different　well　widths　varying　from　2　to　14　nm,　respectively.　The　in-plane　optical　anisotropy　(IPOA)　of　these　samples　are　investigated　by　reflectance　difference　spectroscopy.　It　is　demonstrated　that　the　IPOA　of　the　QW　sample　with　the　ultra-thin　InAs　layer　inserted　at　the　direct　interface　is　larger　than　that　with　InAs　layer　inserted　at　the　inverted　interface,　which　can　be　attributed　to　the　smaller　segregation　effect　of　indium　atoms　at　the　direct　interface　compared　to　that　at　the　inverted　interface　as　confirmed　by　theoretical　calculations　based　on　6　band　k·p　theory.　Our　results　demonstrate　that　indium　atoms　present　different　segregation　lengths　at　the　direct　and　inverted　interfaces　of　GaAs/AlGaAs　QWs.　©　2016　Elsevier　B.V.　All　rights　reserved.