The　in-plane　optical　anisotropy　(IPOA)　in　(001)-grown　GaAs/AlGaAs　quantum　wells　(QWs)　with　different　well　widths　varying　from　2-nm　to　8-nm　has　been　studied　by　reflectance　difference　spectroscopy.　Ultra-thin　InAs　layers　with　thickness　ranging　from　0.5　monolayer　(ML)　to　1.5　ML　have　been　inserted　at　GaAs/AlGaAs　interfaces　to　tune　the　asymmetry　in　the　QWs.　It　is　demonstrated　that　the　IPOA　can　be　accurately　tailored　by　the　thickness　of　the　inserted　ultra-thin　InAs　layer　at　the　interfaces.　Strain-induced　IPOA　has　also　been　extracted　by　using　a　stress　apparatus.　We　find　that　the　intensity　of　the　strain-induced　IPOA　decreases　with　the　thickness　of　the　inserted　InAs　layer,　while　that　of　the　interface-induced　IPOA　increases　with　the　thickness　of　the　InAs　layer.　Theoretical　calculations　based　on　6　band　k　·　p　theory　have　been　carried　out,　and　good　agreements　with　experimental　results　are　obtained.　Our　results　demonstrate　that,　the　IPOA　of　the　QWs　can　be　greatly　and　effectively　tuned　by　inserting　an　ultra-thin　InAs　layer　with　different　thicknesses　at　the　interfaces　of　QWs,　which　does　not　significantly　influence　the　transition　energies　and　the　transition　probability　of　QWs.　©　2015　AIP　Publishing　LLC.