Herein, we report reactive oxygen species (ROS)- and pH-responsive biodegradable polyethylene glycol (PEG)-block-polycarbonate by installing thioether groups onto the polycarbonate and its self-assembled core/shell structured micelles for anticancer drug delivery. Oxidation of thioethers to sulfoxide and subsequently sulfone induces an increase in hydrophilicity, resulting in more hydrophilic micellar core. This phase-change caused the micelles to swell and enhance cargo release. Carboxylic acid groups have also been installed onto thioether-containing polycarbonate to promote loading of amine-containing anticancer doxorubicin through electrostatic interaction. Urea-functionalized thioether-containing PEG-block-polycarbonates were synthesized to mix with the acid-functionalized PEG-block-polycarbonate for stabilizing micelle structure through hydrogen-bonding interaction. The mixed micelles were 50 nm in diameter and had a 25 wt% loading capacity for doxorubicin. Enhanced drug release from the micelles was triggered by low pH and high content of ROS. Drug-encapsulated micelles accumulated in tumors through leaky tumor vasculature in PC-3 human prostate cancer xenograft mouse model.