A spray coated thin film of all-E-poly[(3-methoxy-2,5-thiophenediyl- 1',2'-ethenediyl)(4"-methoxy-2",5"-thiophenediyl- 1",2"-ethenediyl)], a conducting polymer, was analyzed by grazing emission X-ray fluorescence spectrometry. Measuring the S/CI ratio in this sulfur-containing polymer with one terminal chlorine allowed us to determine the chain length and, hence, the molecular weight. The result was in acceptable agreement with that of a well-established method for the determination of the molecular weight of polymeric materials.