Tumor　targeting　and　controlled　drug　release　at　the　target　are　the　key　problems　for　cancer　pharmacotherapy.　A　simply　structured　pH-responsive　nanocarrier　was　prepared　to　achieve　the　above　aims　in　this　study.　A　four-armed　star　copolymer,　tetra-(methoxy-poly(ethylene　glycol)-poly(2-(N,N-diethylamino)ethyl　methacrylate)-poly(e-caprolactone)　pentaerythritol　((mPEG-pDEA-PCL)(4)-PET,　PDCP),　was　synthesized　via　the　ring-opening　polymerization,　atom　transfer　radical　polymerization　and　click　chemistry,　which　formed　a　mono　molecular　nanocarrier　in　water.　Its　size　and　zeta　potential　were　strongly　pH-dependent　from　71　nm　and　2.1　mV　at　pH　8　to　127.5　nm　and　25.4　mV　at　pH　5.　The　morphological　change　of　pDEA　chains　was　the　basic　reason.　The　chains　were　protonated　at　lower　pH　so　as　to　freely　extend　to　the　aqueous　media,　though　they　were　hydrophobic　at　higher　pH　to　coat　on　the　surface　of　hydrophobic　cores.　The　star-shaped　PDCP　had　a　large　hydrophobic　core　to　load　hydrophobic　drugs　(e.g.,　paclitaxel).　High　effective　drug　entrapment　in　the　blood　circulation　and　rapid　drug　release　at　the　tumor　tissues　was　achieved　in　PDCP　due　to　its　pH-responsive　function.　The　MCF-7　cytotoxicity　of　the　paclitaxel-loaded　PDCP　nanocarriers　at　pH　6.5　was　similar　to　free　paclitaxel.　And　the　PDCP　nanocarriers　were　well　internalized　by　the　MCF-7　cells　according　to　the　flow　cytometry　and　laser　confocal　microscopy.　The　paclitaxel-loaded　PDCP　nanocarriers　showed　the　comparable　in　vivo　anticancer　effect　to　the　paclitaxel　solution　(Taxol)　although　the　former＇s　toxicity　was　much　lower　than　the　latter.　The　star-shaped　pH-responsive　monomolecular　PDCP　nanocarriers　are　suitable　to　deliver　hydrophobic　anticancer　drugs　for　cancer　therapy　with　tumor　targeting　and　controlled　drug　release.