High concentrations of adenosine and interleukin (IL)-6 in the tumor microenvironment have been identified as one of the leading causes of cancer growth. Thus, we decided to inhibit the growth of cancer cells by inhibiting the production of adenosine and IL-6 in the tumor environment at the same time. For this purpose, we used chitosan-lactate-PEG-TAT (CLP-TAT) nanoparticles (NPs) loaded with siRNA molecules against CD73, an adenosine-producing enzyme, and IL-6. Proper physicochemical properties of the produced NPs led to high cell uptake and suppression of target molecules. Administration of these NPs to tumor-bearing mice (4T1 and CT26 models) greatly reduced the size of the tumor and increased the survival of the mice, which was accompanied by an increase in anti-tumor T lymphocyte responses. These findings suggest that combination therapy using siRNA-loaded CLP-TAT NPs against CD73 and IL-6 molecules could be an effective treatment strategy against cancer that needs further study.