Epigenetic drugs such as histone deacetylase inhibitors (HDACIs) possess anticancer properties due to its ability to regulate genes associated with tumor growth, differentiation, apoptosis and metastasis. In addition to its apoptotic effect, phenylbutyrate (PB), a carboxylic acid HDACI, inhibited an anaplastic (ATC) thyroid cancer cell line ARO from penetrating a matrigel coated transwell with concomitant suppression of a metastasis-associated gene, matrix metalloproteinase-7 (MMP-7) and stimulation of a transformation suppressor protein, reversion-inducing- cysteine-rich protein with Kazal motifs without affecting MMP-2 expression levels. Direct evidence suggesting MMP-7 down-regulated cancer metastasis came from the observation of a decreased pulmonary metastasis in SCID mice xeno-transplanted with MMP-7-knocked-down ARO cells. In addition, H-89, a protein kinase A inhibitor, remarkably restored the down-regulaed MMP-7 level treated by PB. Thus, the suppressive effect of PB on MMP-7 was partially carried out through H3 phosphoacetylation. To conclude, our findings suggest PB inhibits MMP-7 expression epigenetically through phosphoacetylation of histone proteins, and thereby, reduced invasive ability of an ATC thyroid cancer cell line.