Recent decades have witnessed a breakthrough in onco-immunology with cancer immunotherapy making a remarkable progress with promising therapeutic effects. Immunotherapy is a therapeutic approach that specifically attacks cancer cells by harnessing the host immune response. However, the existence of tumor immune escape and low specificity, limit the application of cancer immunotherapy. Nanocarriers with unique physiochemical properties are now being widely used for improving the anti-tumor effect of multiple cancer immunotherapeutic agents by offering alternate pharmacokinetics profile, site-specific delivery, and an enhanced cellular uptake. Nanocarriers can be engineered to target immunosuppressive tumor microenvironments to restore anti-tumor immune responses. In this review, we discuss the mechanisms of immune escape and how nanotechnology is applied to circumvent immunotolerance and improve anti-tumor immunotherapeutic effects. Perspectives on the rationale for designing nanocarriers-based cancer immunotherapy are also provided.