Thallium (Tl) is a typical trace metal of extreme high toxicity. As a concomitant element, Tl is widely found in various sulfide minerals and K-containing rock minerals. The outburst of Tl pollution in drinking water sources of the northern branch of the Pearl River in China as reported in 2010 has greatly aroused public concerns about Tl pollution in China. Apart from typical sources of Tl pollution such as Pb and Zn smelting and the mining and utilization of Tl-containing pyrite ores, the steel-making industry was discovered a new significant source that contributed to this Tl pollution incidence. Thallium contents in raw materials, fly ash and wastewater collected from a typical steel-making enterprise were determined by inductively coupled plasma mass spectrometry (ICP-MS). The results showed that Tl contents (0.02-1.03 mg/kg) are generally low in the raw materials, while fly ash samples have generally enriched Tl levels (1.31-6.45 mg/kg). Wastewater obtained from the dedusting process of the sintering furnace also exhibited excessive Tl levels (574-2130 μg/L). All these results suggested a possible release and gasification of Tl compounds from the raw materials under high temperatures (>800ºC) during the sintering processes, which were then accumulated in the flue gas and fly ash and washed into the wastewater by wet dedusting. Lime precipitation method is not effective for removing Tl from wastewater, since Tl mostly is present as dissolved Tl+ in the water. The study initiated a preliminary design of a fast and effective treatment method for Tl removal from Tl-containing industrial wastewater by using a deep oxidation system.