The crystal structure of a "coplanar" polychlorinated biphenyl (PCB) derivative, 4-methoxy-3, 3', 5'-trichlorobiphenyl (C13H9Cl3O), is described. The torsion angle of the title compound is 41.31(07) degrees, which is in good agreement with the calculated torsion angle of 38.2 degrees in aqueous solution.