NOVELTY - Preparing (I) dioxin decomposer from Stevia, comprises forcibly fermenting leaf and stem concentrate of S. rebaudiana Bertoni, separately using ultrasonic waves in the presence of cultured Stevia yeast (zymogen), concentrating forcibly fermented solution by further fermentation, mixing the fermented leaf and stem concentrate and re-fermenting the mixture using ultrasonic waves.    USE - The dioxin decomposer comprises fermented leaf and stem concentrate at a volume ratio of 4:6 suitable for use in decomposing dioxins of food, feedstuffs, fertilizers and cosmetics and at a volume ratio of 2:8 suitable for use in decomposing dioxins incurred in incineration. The dioxin decomposer diluted with 10-100 volumes of water when immediately applied to a subject to be treated, at 2-20 cc/g of the subject is useful for decomposing dioxins (claimed).    ADVANTAGE - The decomposer is very effective for decomposing dioxins or chlorine-containing toxin materials like dioxins, at room temperature without being processed additionally. The decomposer does not require complex reaction controlled processes and does not cause regeneration of dioxins during reaction. The forcible fermentation using ultrasonic waves rapidly removes offensive odor and toxicity from Stevia extract.    DETAILED DESCRIPTION - (I) Involves extracting useful ingredients by steeping crushed dry leaves and stems of S. rebaudiana Bertoni, separately, in water at 5-10 l of water/kg of the crushed plant, where the leaves and stems have a water content of 6% or less, filtering the leaf extract and the stem extract and concentrating the supernatants, in a multistage manner at 80-150degreesC to give a leaf concentrate with a saccharinity of 20-30degrees and stem concentrate with a saccharinity of 15-25degrees, culturing Stevia yeast (zymogen) in sludge obtained after the extraction, forcibly fermenting the leaf concentrate and the stem concentrate, separately using ultrasonic waves in presence of 0.1-2 volume% of cultured Stevia yeast, concentrating the forcibly fermented leaf and stem solution by further fermenting them for 3-6 months and mixing the leaf concentrate at volume ratio of 2:8-4:6 with the fermented concentrate and re-fermenting the mixture using ultrasonic waves.    An INDEPENDENT CLAIM is also included for a dioxin decomposer prepared by the above method.