A　promising　theranostic　platform　for　solid　tumors　would　deliver　and　release　anticancer　nanomedicine　effectively　in　tumor　cells.　However,　diverse　biological　barriers,　especially　related　to　the　tumor　microenvironment,　impede　these　theranostic　agents　from　reaching　the　tumor　cell.　Herein,　a　sequential　pH　and　reduction-responsive　polymer　and　gold　nanorod　(AuNR)　core–shell　assembly　to　overcome　these　barriers　via　a　two-stage　size　decrease　and　disassembly　of　the　nanoplatform　responding　to　the　specified　tumor　microenvironment　are　reported.　The　tumor　uptake　of　the　hybrid　nanoparticle　(NP)　is　14.2%　ID　g−1,　which　is　two　and　four　times　higher　than　the　noneresponsive　hybrid　NPs　and　small　AuNR@PEG,　respectively.　After　tumor　uptake　of　the　hybrid　NPs,　the　disassembled　ultrasmall　AuNRs　coated　with　a　polymer　of　polymerized　reduction-responsive　doxorubicin　(DOX)　prodrug　monomers　penetrate　into　the　solid　tumor　and　lead　to　localized　DOX　release　in　the　tumor　cell.　A　linear　increase　in　photoacustic　(PA)　effects　from　the　PA　activating　polymer　on　an　AuNR　cluster　surface　indicates　a　critical　role　of　electromagnetic　fields　in　the　AuNR　assembly,　which　is　consistent　with　the　theoretical　calculation　results.　Furthermore,　the　hybrid　NP　can　serve　as　a　promising　deep-tissue　PA　and　surface-enhanced　Raman　scattering　imaging　agent　for　real-time　in　vivo　investigation　of　physiological　behaviors　and　deep　tumor　penetrating　nanotherapy　effects.　©　2019　WILEY-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim