Replacement　of　downregulated　tumor-suppressive　microRNA　(Ts-miRNA)　is　recognized　as　an　alternative　approach　for　tumor　gene　therapy.　However,　in　situ　monitoring　of　miRNA　replacement　efficacy　in　a　real-time　manner　via　noninvasive　imaging　is　continually　challenging.　Here,　glutathione　(GSH)-activated　light-up　peptide-polysaccharide-inter-polyelectrolyte　nanocomplexes　are　established　through　self-assembly　of　carboxymethyl　dextran　with　disulfide-bridged　(＂S-S＂)　oligoarginine　peptide　(S-Arg(4)),　in　which　microRNA-34a　(miR-34a)　and　indocyanine　green　(ICG)　are　simultaneously　embedded　and　the　nanocomplexes　are　subsequently　stabilized　by　intermolecular　cross-linking.　Upon　confinement　within　the　robust　nanocomplexes,　the　near-infrared　fluorescence　(NIRF)　of　ICG　is　considerably　quenched　(off)　due　to　the　aggregation-caused　quenching　effect.　However,　after　intracellular　delivery,　the　disulfide　bond　in　S-Arg(4)　can　be　cleaved　by　intracellular　GSH,　which　leads　to　the　dissociation　of　nanocomplexes　and　triggers　the　simultaneous　release　of　miR-34a　and　ICG.　The　NIRF　of　ICG　is　concomitantly　activated　through　dequenching　of　the　aggregated　ICG.　Very　interestingly,　a　good　correlation　between　time-dependent　increase　in　NIRF　intensity　and　miR-34a　replacement　efficacy　is　found　in　nanocomplexes-treated　tumor　cells　and　tumor　tissues　through　either　intratumoral　or　intravenous　injections.　Systemic　nanocomplexes-mediated　miR-34a　replacement　significantly　suppresses　the　growth　of　HepG-2-　and　MDA-MB-231-derived　tumor　xenografts,　and　provides　a　pronounced　survival　benefit　in　these　animal　models.