Abstract: Novel durable 2-part hair dyeing agents composed of a first agent comprising as essential components at least one compound that forms HCO.sub.3 --by dissociation in water, an alkali generating substantially no irritating odor and a dye for hair and having a pH of 8.2 to 9.0. and a second agent comprising as essential components hydrogen peroxide and a buffer solution and having a pH of 2.0 to 4.0, the weight ratio of the first agent and the second agent to be mixed being such that the pH of the mixture of the two is in a range of from 6.5 to 7.9. These 2-part hair dyeing agents require only a short dyeing time, create little damage to hair and no irritating or disagreeable odor and have high dyeing effect.