Photodynamic therapy (PDT) has emerged as a more effective and promising treatment towards cancer therapy. PDT is a minimally invasive and spatially selective medical technique to destroy cancer cells without drug resistance, which has been increasingly applied in the clinical praxis alongside surgery, chemotherapy and radiotherapy. However, traditional PDTs use a high energy one-photon laser beam, which is far from the efficient optical window of mammalian tissue (650-950 nm). Moreover, it has great limitations in the depth of penetration, and induces the undesired light toxicity. The development of photosensitizers has always been a bottleneck to the effective application of PDT in clinical practice. From the first generation of hematoporphyrin derivatives to the third-generation photosensitizers with tumor targeting ability, they meet the urgent clinical needs to some extent, but they still can not satisfy the requirements of two-photon PDT. Therefore, the development of photosensitizers, which are capable of two-photon activated PDT, has become a promising approach. Among the various two-photon absorption photosensitizers, ruthenium (Ⅱ) polypyridyl complexes have been recognized as excellent candidates due to their attractive photophysical properties. This review is prepared to summarize the recent achievements in the application of ruthenium (Ⅱ) polypyridyl complexes as photosensitizers for two-photon PDT, as well as to provide guidance for the design of two-photon activated photosensitizers in future research.