Compared to normal cells, there is a relatively high level of reactive oxygen species (ROS) in tumor cells caused by defecting ROS scavenging systems. To this issue, developing ROS‐responsive nanocarriers has been a promising way to cancer therapy. However, it is always difficult for a certain ROS‐responsive nanocarrier to be perfectly triggered due to the complexity of cancerous tissues. Thus, it is pressing to improve the response sensitivity of ROS‐responsive nanocarriers. Herein, the Fenton‐like reaction enhanced ROS response of polymeric nanocarriers of an iminoboronate backbone‐based hyperbranched polymer with metallisable 8‐hyroxyquinoline (HQ) moieties is demonstrated. HQ‐Cu catalytic sites can be formed at the prepared nanocarriers via the complexation of Cu(II) ions and HQ moieties. Upon H2O2, hydroxyl radicals (·OH) are quickly generated via the Fenton‐like reaction between H2O2 and HQ‐Cu. Then, the oxidative cleavage of iminoboronate moieties can be effectively activated to disrupt the nanocarriers, leading to a rapid release of encapsulated drugs. It is proposed that this kind of polymeric nanocarriers with Cu‐complexed catalyzing‐triggered ROS response may achieve highly effective oxidation therapy.