In 2018, “negative ion powder” mattress produced by a South Korean manufacturer producing a dose rate of > 1 mSv/year, was found to have monazite powder in it. In order to verify if other products advertised as containing “negative ion powder” were also hazardous, an investigation had been carried out by the Atomic Energy Council and Institute of Nuclear Energy Research in Taiwan. By the end of April 2019, 11 kinds and a total of 59 samples were inspected for radon content. The radiation doses for the samples were evaluated using Atomic Energy Council approval evaluation setup which was established according to the characteristics of the products. The highest concentration of 220Rn among the inspected mattresses was over 10 kBq/m3 and the evaluated annual dose was about 78.5 mSv. The linearity of the surface dose rate and the measured thoron gas concentration for the mattress samples was also discussed in this study.