This study investigated the effects of tetrachloroethene (PCE) on radon measurements that employed the liquid scintillation counting (LSC) method referring to 7500-Rn B of Standard Methods for the Examination of Water and Wastewater. Laboratory-produced radon-enriched water was used to compare the counting rates of the radon water with and without PCE addition, and groundwater samples from a site contaminated by chlorinated solvents were used to investigate the application of the laboratory experiments. The results showed that the major factor reducing counting efficiency was resulted from the interaction between PCE and a cocktail through the quench effect. The counting rate showed an exponentially decreasing trend when PCE addition was increased. The results indicated that a small addition of PCE reduced the counting rate considerably. An alternative energy channel 500-1000 to the optimal channel was suggested to attenuate the quench effect on radon measurement. The quench effect was also observed on samples from a site contaminated by chlorinated solvents. The concepts and procedures presented in this study are a reference for future research on the topic of chlorinated solvents or other quench chemicals involving in radon measurement.