Cancer is one of the most devastating disorders of the 21st century, creating a major concern among clinicians and researchers. Many different treatment strategies are being tried to fight the war against cancer have been tested. Various inorganic nanoparticles have been investigated to induce cytotoxicity in cancer cells and one of the successfully tried nanoparticles is Selenium Nanoparticles (SeNPs). Green synthesized SeNPs are a promising source of new antioxidant and anti-inflammatory agents, given the multiplicity of its mechanism. SeNPs displayed antiproliferative potential against colon, liver, cervical, breast, melanoma, and prostate cancer cells by several mechanisms, including triggering apoptotic signal transduction pathways or slow down the angiogenic signalling in cancer cells. Metal nano-therapies such as SeNPs are granted research consideration for cancer treatment. The biocompatibility achieved through green synthesis suggests its possible use not only in specific cancer conditions but also in other types of cancer without any risk of toxicity of these molecules.