The Korea Laboratory Accreditation Scheme (KOLAS) operates accreditation programs for ensuring measurement traceability withthe International System (SI) of Units – the highest calibration standard that measurements can be tested against. As of September 2023,there are 70 KOLAS-accredited laboratories in the Republic of Korea that specialize in humidity calibration. Among them, 32 KOLASlaboratories, along with one laboratory not affiliated with KOLAS, participated in the proficiency test (PM 2023-11) for relative humiditytransducers in 2023. This proficiency test was conducted within a relative humidity range of 20–90% at a temperature of approximately20 °C, taking into consideration the calibration and measurement capability (CMC) of the participating laboratories. The primaryobjective of the proficiency test was to establish the measurement equivalence between each participating laboratory and the referencelaboratory, by calculating the number of equivalence (En). When |En| was less than 1, the measurements from the participating and referencelaboratory were equivalent. Out of the 33 participating laboratories, 32 successfully met this criterion and passed the proficiencytest.