Devitalization has been widely used in the root canal therapy of primary and permanent teeth in China more than ten years ago. With the development of local anesthetic drugs and injection technologies, this treatment method with high potential risks has been gradually abandoned. However, a questionnaire survey targeted all the participants at the 2018 China Pediatric Dentistry Conference showed that the devitalizer utilization proportion was still as high as 38.1% (383/1 005), even though the ratio was much lower than 75.5% (105/139) in 2003. These doctors had pay more attention to tissue burn caused by devitalizer marginal leakage or direct leakage, and know how to identify and handle with devitalizer burn. Devitalizers were usually made of arsenic trioxide, metal arsenic or paraformaldehyde, which have cytotoxicity, allergenicity, mutagenicity, carcinogenicity, and teratogenic effects on animals. Marginal leakage of devitalizers have high risks of causing soft and hard tissue necrosis. Most of the dentists have an understanding of the potential damages of arsenic-containing devitalizers, so they will choose parafor-maldehyde with relatively less toxicity. Paraformaldehyde has a certain self-limitation, and there are few cases reported, so some dentists lack of vigilance. Paraformaldehyde can also causes tissue necrosis if leakage happens, and the treatment methods are similar to that of arsenic-containing devitalizers. When handling with devitalizers burn, the necrosed soft and hard tissue, for example gingiva, alveolar bone or teeth that cannot keep, must be completely removed until fresh blood appears, then rinse with large amount of saline and seal with iodoform gauze. This paper described two cases of devitalizer burn during the root canal treatment of primary molars, both of the doctors failed to identify the devitalizer burn symptoms in the early stage, thus didn’t do proper treatments immediately after burning. Resulting in the necrosis of large area of gingiva and alveolar bone, loss of primary molars and permanent tooth germs 1-2 months after devitalizer burn. This paper reported these two cases in detail in order to warn dentists the high risks of using any kind of devitalizers, help them learn how to identify and treat devitalizer burn, and remind them to stop using devitalizers as soon as possible.