We evaluated the antibacterial activities against Staphylococcus aureus of cotton fabrics dyed with water extracts from 16 species of wild grasses on the basis of “JIS L-1902 Test Method”. (1) After 18 h of cultivation, the viable counts of the cotton fabrics dyed was from 3.1 × 10² to 3.0 × 10⁵ cells, and fewer than the viable counts (2.9 × 10⁷ cells) of the standard cotton fabrics without dyeing. Above all, the cotton fabrics dyed with extracts from Vitis saccharifera, Oenothera biennis, Commelina communis, Reynoutria japonica and Eupatorium lindleyanum had high antibacterial activities. (2) Bacteriostatic activities and bactericidal activities of 16 kinds of cotton fabrics dyed were measured, and so bacteriostatic and bactericidal activities of all samples were more than 3.0, and 0.9, respectively. However, the correlation wasn't shown between these activities and minimum inhibitory concentration of extracts against the growth of S. aureus .