Encapsulation of small-molecule drugs in hydrophobic polymers or amphiphilic copolymers has been extensively used for preparing polymeric nanoparticles (NPs). The loadings and loading efficiencies of a wide range of drugs in polymeric NPs, however, tend to be very low. In this Communication, we report a strategy to prepare polymeric NPs with exceptionally high drug loading (>50%) and quantitative loading efficiency. Specifically, a dimeric drug conjugate bearing a trigger-responsive domain was designed and used as the core-constructing unit of the NPs. Upon co-precipitation of the dimeric drug and methoxypoly(ethylene glycol)-block-polylactide (mPEG-PLA), NPs with a dimeric drug core and a polymer shell were formed. The high-drug-loading NPs showed excellent stability in physiological conditions. No premature drug or prodrug release was observed in PBS solution without triggering, while external triggering led to controlled release of drug in its authentic form.