Abstract: Allium cepa L., from Latin cepa “onion” is a vegetable and is the most cultivated species of the genus Allium. A traditional fermented tea leaf (Camellia sinensis var. assamica) and fresh tea leaves of C. sinensis var. assamica are conventionally used as the raw material for Miang fermentation in Thailand. In this study, using various mordants, color changes to fabric silk were compared with the dye of the coat of onion and C. sinensis var. assamica-fermented leaf. The 300 g of the coat of onion was dissolved into 12 L of distilled water. For a natural dye from dried C. sinensis var. assamica-fermented leaf, its extraction was also performed with two steps as the coat of onion. Mordants of copper acetate, aluminum potassium sulfate, sodium tartrate plus citric acid, iron (II) sulfate or potassium dichromate were pre-mordanted with the fabric silk for both dyes from the onion and tea. Only onion dye stained the silk traditional brown without any mordant which was similar color with the dried coat of onion. Copper acetate and potassium dichromate showed very similar colors with “none” but darkness or brightness was shown. Very interestingly, iron (II) sulfate induced near black which was completely different from the only staining by onion dye without any mordant. Original color without any mordant of “none” represented brownish in the staining of C. sinensis var. assamica-fermented leaf. In particular, aluminum potassium sulfate induced very clear shiny yellow and iron (II) sulfate did the mix of brown and gray. This study would be useful to comparatively analyze the staining changes by the coat of onion and C. sinensis var. assamica-fermented leaf. Further study will be processed to evaluate them as a biological usage.