Many studies have discussed the biotreatment of ethanethiol (ET) under aerobic conditions. However, O-2 free conditions offer bio-conversion of ET gas into elemental sulphur and/or sulphate using as electron acceptor, and this has been not studied. In this study, an anoxic biotrickling filter was tested in lab-scale conditions with ET/ ratio 0.74 and 0.34 mole/mole to remove malodorous ET waste gas. The study examined the effect of three operational parameters: ET inlet concentrations (150, 300, 800, and 1500 mg/m(3)), trickling velocities (0.12, 0.18, 0.24, 0.3, and 0.45 m/h), and empty bed residence times (30, 60, 90, and 120 s). It found that the effect of trickling velocity on removal efficiency depended on inlet concentrations; 0.24 m/h trickling velocity resulted in efficient ET removal (higher than 90.8% for 150 mg/m(3) of inlet concentration) while 0.45 m/h trickling velocity could only achieve a removal of 80.6% for 1500 mg/m(3) of inlet concentration at fixed EBRT 60 s. Increasing the EBRT up to 60 s was adequate to achieve removal efficiency, i.e. 92 and 80% for ET inlet concentrations 150 and 1500 mg/m(3) respectively, and the maximum elimination capacity was 75.18 g/m(3)/h at 0.45 m/h. Overall, the anoxic conditions enhanced the low oxidation rates of ET in an anoxic biotrickling filter despite mass transfer limitations and poor solubility of ET.