Despite the advancement in cancer therapy, a high number of patients fail treatment because of drug resistance. Several preclinical in vitro data suggest that phenylbutyrate has antiproliferative, antiangiogenic, antimetastatic, immunomodulatory, and differentiating properties. Moreover, phenylbutyrate administration in vivo provided an oncoprotective effect. However, the results of clinical trials indicate that the antineoplastic potential of phenylbutyrate is hindered by its pharmacokinetic and pharmacodynamic properties. Thus, understanding the exact mechanisms of the anticancer effect of phenylbutyrate could assist in the selection of patients who will best benefit from this drug. The present review discusses the proposed mechanisms of antineoplastic effect of phenylbutyrate and the preclinical and clinical evidence suggesting its potential role as anticancer in different types of cancer.