Pentachlorobenzene (PeCB) is an aryl chloride and a five-substituted chlorobenzene with the molecular formula C6HCl5 which is a chlorinated aromatic hydrocarbon.

Since PeCB is generally produced in small quantities in the chlorination of benzene, it is also contained in other chlorobenzenes (dichlorobenzenes, trichlorobenzenes etc.)

Today, a majority of the PeCB released into the environment is a result of backyard trash burning and municipal waste incineration.

[4] PeCB was a component of a mixture of chlorobenzenes added to products containing polychlorinated biphenyls in order to reduce viscosity.

[1][4] Consequently, pentachlorobenzene was added in 2009 to the list of chemical compounds covered by the Stockholm Convention, an international treaty which restricts the production and use of persistent organic pollutants.