Lectins are proteins or glycoprotein’s of non-immune origin that exhibit specific binding affinity for the carbohydrate moiety of glycol-conjugates. Several plant lectins have been shown to induce cell death in cancer cells, suggesting that these molecules may have applications in cancer treatments. Cancer cells are known to express and/or secrete glycol-conjugates with an aberrant glycan structure. Thus, lectins may detect such changes, leading to their use in cancer diagnosis and cancer-specific treatment. Mistletoe lectins are representative of an anticancer drug target, and lentil lectin has been shown to have diagnostic applications in hepatocellular carcinoma. In this review, we describe recent progress in lectin researches, with special emphasis on the applications of plant lectins in human cancer diagnosis and therapy.