During conventional chemotherapy for cancer, nonspecific drug distribution, which causes serious side effects in normal tissues, is a serious limitation. Thus, it is desirable to develop a tumor or intracellular microenvironment-responsive nanosystem for targeted and on-demand drug release. In the present study, we engineered an intelligent pH-activatable nanosystem, in which a gadolinium-doxorubicin-loaded nanoscale coordination polymer (Gd-Dox NCPs) was the core and hyaluronic acid was the targeting shell. Taking advantage of CD44 receptor-mediated recognition, the nanoparticles were internalized selectively into human cervical carcinoma (HeLa) cells, and trapped within acidic compartments where the fluorescence of Dox recovered, along with the acid dismantling of the Gd NCPs, allowing real-time monitoring of drug release. In vitro experiments also showed that the Gd NCPs present enhanced T₁ signals after acid-triggered degradation, suggesting their potential use as contrast agents for magnetic resonance imaging. Such nanocarriers, which feature high biodegradation, selective targeting ability, and rapid response to stimulus, demonstrated enhanced therapeutic efficacy in targeted cancer cells and "turned on" T₁ signals in vitro, showing great promise for diagnosis and treatment.