We have examined the decomposition of naphthalene, anthracene, pyrene and coronene at high pressures and temperatures. Experiments were performed using in situ X-ray diffraction in multianvil apparatus at the SPring-8 synchrotron radiation facility. In the pressure range of 1.5–3.7 GPa decomposition of studied polycyclic aromatic hydrocarbons (PAHs) was detected at 773–973 K. Melting was identified only for naphthalene at 727–730 K and 1.5 GPa. Quenched products analyzed by Raman spectroscopy consist of nano- and microcrystalline graphite. The triple points between solid, liquid and carbonized (decomposed) PAHs were placed at 1–2 GPa and 800–850 K. Analyses of P-V-T data indicate that anthracene and coronene possess very low thermal expansion at 1.3–4.2 GPa. The obtained melting and decomposition parameters for PAH restrict PT-conditions of their formation by local impacts during early planetary history, as well as provide evidences for secondary origin of PAH inclusions in natural mantle minerals from kimberlites.