Although the indications for immune checkpoint inhibitors are expanding rapidly, the disease will eventually progress in many patients. Elucidating and overcoming the resistant mechanisms to immune checkpoint inhibitors is a major challenge. WNT/β-catenin pathway has long been known as one of the mechanisms involved in cell proliferation and epithelial-mesenchymal transition in cancer development. Recently, it has become clear that WNT/β-catenin pathway also plays a role in cancer immune escape, as reported in melanoma. We have also studied WNT/β-catenin pathway as a mechanism of immune escape in lung cancer. In this article, we review how WNT/β-catenin pathway is involved in immune escape and resistance to immune checkpoint inhibitors, mainly in non-small cell lung cancer. In addition, we discuss how to overcome the tumor immune mechanism caused by WNT/β-catenin pathway in the context of current combination therapies and therapies in development.