In this study, synthetic fiber fabrics such as polyester, nylon 6, acrylic and acetate were dyed with indigoid vat dye. The effects of the composition of alkaline reduction, dyeing time and dyeing temperature on color strength and color fastness of the fabrics were investigated. Also the color fastnesses to wash and light of the dyed fabrics were studied. In dyeing of polyester, nylon, acrylic and acetate fiber fabrics with indigo vat dyes, it appears that these fabrics have high values of K/S up to Ig/L of sodium hydroxide and 6g/L of reducing agent. Indigo vat dyeing for synthetic fiber fabrics was verb fast, and lead to dyeing equilibrium within twenty minutes. The K/S values of dyed fabrics did not changed in dye concentration more than 10% o.w.f.. Synthetic fiber fabrics dyed with indigoid dyes had bad light fastness.