In the standard analysis model of the Xenon worth in thermal reactors, Xe-135m has been neglected due to its short half-life (15.29 min).The impact of Xe-135m during a transient was briefly analyzed usingpoint reactor model with the TENDL-2011and TENDL-2013 datathat it will lead the Xenon worth to be in-creased.These results are then applied tothe PCRmeasurementbased on the measured data from Wolseong2 reactor in order to analyze the potential impacts of Xe-135m on the PCR of CANDUreactors.When the Xenon worth is increased, the measuredPCR is generally decreased by0.54pcm/%Pwith TENDL-2011, and by 0.20pcm/%P with TENDL-2013on average.