The purpose of this study is to investigate the dyeing property of gromwell on modified cotton fabric by chitosan. Modified cotton fabrics were manufactured by crosslinking agent epichlorohydrin in the presence of chitosan. Gromwell colorants were extracted with methanol. Modified cotton fabrics dyed using gromwell were post-mordanted using Al, Fe and Cu. The dyeability (K/S) and color factors (L, a, b, ${Delta}E$ and h) of modified cotton fabrics were measured by computer color matching. Additionally the fastness to washing and light were also investigated. The dye-uptake of modified cotton fabrics increased with the dyeing time. The saturated dyeing time was about 10minutes at $50^{circ}C$. The dyeability (K/S) was remarkably increased with increasing content of chitosan because of having a amine group of chitosan. Modified cotton fabrics were dyed yellowish red by non and Fe mordanting, blueish red by Al and Cu mordanting, respectively. The washing fastness of non, Al, Fe and Cu mordant in the presence and absence of chitosan were increased $1{ ightarrow}2$, $3{ ightarrow}4$, $4{ ightarrow}4-5$ and $4{ ightarrow}4-5$ respectively. And light fastness of non, Al, Fe and Cu mordant in the presence and absence of chitosan were increased $1{ ightarrow}1-2$, $1{ ightarrow}1-2$, $1.2{ ightarrow}2.3$ and $1-2{ ightarrow}2$ respectively.