This study was conducted to assess oxygen uptake characteristics of soil microcosm for biodegradation of sulfolane and thiolane mainly observed in a waste disposal site. The microcosm was obtained from the site and then spiked with nutrients and levels of contaminants (i.e. thiolane and sulfolane) in a closed vessel. The amount of oxygen consumed for sulfolane was peaked at 1450 μL for 200 mg/l and then decreased at greater than 500 mg/l. Sulfolane was completely degraded below 40 mg/l. It indicates that longer period of adaptation would be needed to completely degrade at greater than 500 mg/l. Apart from, the highest oxygen consumption was accomplished at 38.5 μL for 1 mg/l of thiolane, but it was dropped to a negligible level for 20 mg/l. That is, increasing thiolane concentration correspondingly decreased oxygen demand due to its inhibition against microcosm. Nevertheless, the unit amount of oxygen consumption for thiolane was well proportional to the cumulative oxygen uptake. It is concluded that sulfolane can be readily biodegradable in an aerobic condition, while degradation of thiolane was considerably inhibited against the given soil microorganisms even though its concentration was extremely lower by hundredths than that of sulfolane.