The linewidth of parametric X-ray radiation has been determined experimentally applying an absorption technique. Using a copper foil of 27.7 μm thickness and tuning the energy of the PXR peak across the K-absorption edge of copper by tilting a 55 μm thick diamond crystal, the variance of the PXR line at 8.98 keV photon energy was found to be σ = 48 eV. The diamond crystal has been bombarded with electrons of 6.8 MeV kinetic energy delivered by the superconducting linear accelerator S-DALINAC at Darmstadt. The experimental yield of the intensity amounts to N = 0.91 10 - 5 photons/(electron sr). From the measured variance the spectral density in the peak is deduced to be J = 0.95 10 - 7 photons/(electron sr eV).