A tailor-made traceable pH-sensitive drug delivery system based on polyurethane (PU) microcapsuleswas fabricated using a facile double-emulsion method containing 3,3-dioctadecyloxacarbocyanine per-chlorate, doxorubicin (DOX) and sodium bicarbonate (NaHCO3). When PU microcapsules were immersedin acidic media, NaHCO3could react with the H+to quickly produce CO2bubbles to puncture the PU shell,resulting in rapid release of DOX to promptly reach the intracellular drug therapeutic threshold to killcancer cells in a short period. Confocal laser scanning microscopic analysis showed that these traceablepH-sensitive drug carriers can be easily internalized by BGC 823 and Hela cells, and the loaded DOX canquickly release from PU microcapsules in the endo-/lysosomes to be mainly resided in cell nuclei. Thistraceable pH-sensitive drug carrier can achieve on-demand controlled release profiles for visualizationof cancer therapy. Thus, it is a potential candidate for anticancer drug delivery system in advanced cancertherapy.