Abstract: This paper describes some experiments? on the monitoring of tritium oxide inthe effluents of the HWR's stack. The experimental data showed that the equipment can detect 4×10~3 Bq·m~(-3)HTO in air with the presence of argon-41 which has a concentration of about 1×10~5 Bq·m~(-3). The counting rates caused by HTO and ~(41)Ar in the detector aremeasured separatly. The differences of the HTO concentrations in air under thetwo circumstances of the "on operation" and "shut down" of the HWR are com-pared each other. In addition, the advantages and disadvantages of the equipmentare discussed briefly.