Disclosed is a hair-dyeing composition comprising geraniintannin and a water-soluble iron salt and optionally containing one or more selected from tannic acid, L-cysteine and salts thereof, sodium hydrogen sulfite, sodium sulfite, hydrolyzed product of collagen and resins for hair. The composition may be in the form of either a one-solution-type or a two-solution-type. Also disclosed is a hair-dyeing method using the said composition. The hair dyed with the composition has an almost natural and fast black color.