Six kinds of radioactive organic liquid wastes were incinerated by using city gas. The test liquid wastes were methanol simulated as a low heat of combustion waste, xylene simulated as a high heat of combustion waste, and 4 kinds of wastes of unknown composition. Combustion temperature was monitored by using a thermocouple sensor. Temperature variations were classified into five types: stable pattern, increasing pattern, decreasing pattern, vibrating pattern and the mixed pattern. Stable pattern wastes were burned most efficiently. The other four patterns can be changed to a stable pattern by controlling the gas flow rate.