The clinical application of gemcitabine is limited by hydrophilicity and low plasma half-life. Herein, we developed a chitosan-based nanogel to provide controlled release of gemcitabine and relieve its hydrophilicity. Moreover, the chitosan nanogel is decorated with an alginate polyanion for pH-dependent and more controlled drug release. The effect of different variables on the polyelectrolyte reaction was evaluated using the Box–Benkehen design. The optimum formulation was determined based on higher encapsulation efficiency and loading capacity using HPLC analysis. In the light of the results, this synthesized nanogel has a diameter of around 150 nm and a polydispersity index of 0.344 and provides an acidic pH-dependent release profile. As a result of retaining the ability of cellular uptake, nanogel-loaded gemcitabine led to the cell cycle and apoptosis induction in MCF-7 breast cancer cells, followed by a considerably decreased half-maximal inhibitory concentration (IC50) of cell proliferation compared to free gemcitabine. Based on these results, the chitosan–alginate nanogel can be applied as a pH-dependent platform for the more controlled release behavior of gemcitabine.