Flavonoids belong to polyphenolic secondary metabolites with broad-spectrum pharmacological activities and extensive biological effects, and the most prominent activity is their potential role as anticancer agents. In recent years, flavonoids and their synthetic analogues have been intensely investigated in the treatment of ovarian, breast, cervical, pancreatic, and prostate cancer. To some extent, chemical structures of flavonoids will influence their anticancer activities. Thus, some new analogues based on the structural skeleton of these flavonoids have been synthesized and investigated. This review presents recent advances on the aspects of the natural flavonoids and their synthetic analogues in the treatment of cancers, and new synthetic approaches and possible structure-activity relationships of flavonoids are also briefly summarized.