This review deals with cytotoxic and antiproliferative activity of fifty seven prenylated phenols isolated from Morus alba. Prenyl side chain, which can be variously modified, increases lipophilicity of the substances, thereby improving their penetration through biological membranes and thus results in an increased bioavailability. The objective was to describe the relationship between structure of the prenylated phenols and their cytotoxic effect and to clarify various mechanisms by which cytotoxic prenylated phenols induce apoptosis. The conclusions showed that the cytotoxicity of the substances increases with increasing number of the prenyl side chains and ketal groups. Conversely, modification of the prenyl side chain, such as hydroxylation, reduces cytotoxicity. The cytotoxic activity is also influenced by the presence of prenyl and hydroxyl groups at specific positions.