Self-assembly of stimuli-responsive polymeric nanoparticles have attracted great attention in recent years due to their prospective biological applications. This paper developed a novel pH-sensitive amphiphilic dendritic polyrotaxane drug-polymer conjugate by covalently linking doxorubicin (DOX) and dendritic polyrotaxane via a pH-responsible hydrazone bond with 1.84 wt% (weight percent) of DOX. The drug-polymer conjugate was amphiphilic and could be self-assembled to micelles (PR-g-DOX micelles) in an aqueous solution. The globular morphology and compact micelles with a diameter of around 110 nm were observed by SEM and TEM. Moreover, the micelles showed a significantly faster DOX release at mildly acidic pH of 6.0 and 5.0 and almost no burst release at the physiological pH of 7.4. Notably, it was confirmed that this micelle could efficiently deliver DOX to the nuclei of the tumor cells, which led to a much greater cytotoxic effects in the A549 cancer cells than the parent DOX. In vivo results revealed better drug tolerability of PR-g-DOX micelles and a higher in vivo efficacy without any increase in the toxicity of the PR-g-DOX micelles. Furthermore, the maximum tolerated dose (MTD) results showed that PRg-DOX micelles showed an excellent safety profile with a two-fold higher MTD (10 mg kg(-1) DOX) than that of free DOX (5 mg kg(-1) DOX). We are convinced that the PR-g-DOX micelle has tremendous potentials for targeted cancer therapy.