The development of thermo-responsive and reduction-sensitive polymeric micelles based on an amphiphilic block copolymer poly[(PEG-MEMA)-co-(Boc-Cyst-MMAm)]-block-PEG (denoted PEG-P-SS-HP) for the intracellular delivery of anticancer drugs is reported. PTX, as model drug, was loaded into the PEG-P-SS-HP micelles with an encapsulation efficiency >90%, resulting in a high drug loading content (up to 35 wt%). The PTX-loaded PEG-P-SS-HP micelles show slow drug release in PBS and rapid release after incubation with DTT. The PTX-loaded micelles display a better cytotoxic effect than the free drug, whereas empty micelles are found to be non-toxic. The thermo-responsive and reduction-sensitive polymeric micelles described may serve as promising carriers for cytostatic drugs.