Research to dyeing properties of Ulmi cortex extract, silk and cotton fabrics were dyed and mordanted. Dyes were extracted from distilled water according to different pH values. The dyeability of Ulmi cortex extract were evaluated by conditions of dyeing temperature, dyeing time, dyeing pH, mordanting temperature, mordanting time, mordanting concentration and color fastness, etc. IR spectrum possessed absorption band of -OH at $3400cm^{-1},;C-H;at; 2940cm^{ -1},;aromatic;C=C;at;1628cm^{-1},;1518cm^{-1},;C-O;at; 1107cm^{ -1},;1043cm^{-1}$. And the $labmda$max of extract appeared at 220nm and 280nm, so the substance of Ulmi cortex extract were catechin and tannin. Surface color of dyed fabrics were reddish yellow~yellow~greenish yellow. From the color fastness test, the fabrics dyed with PH 7 extract were excellent in irradiation and washing. Mordanting improved the color fastness and K/S value of dyed fabrics.