To provide a two-pack hair dye or a two-pack decolorant, each of which is composed of a first liquid containing an alkali agent and a second liquid containing an oxidizing agent, the two-pack hair dye or a two-pack decolorant each being composed of the first liquid and the second liquid which are both in liquid state and are easily mixed with each other, and each have a viscosity with which the first liquid and the second liquid do not sag and drip when applied by using user's own fingertips or hands.

Both of a first liquid and a second liquid are made to be in a liquid state, and to be easily mixed with each other, and a viscosity of 60,000-150,000 mPa s with which the first liquid and the second liquid do not sag and drip in use is obtained, by making the first liquid contain 25-50 wt.% of a nonionic surfactant, and the second liquid contain 0.1-10 wt.% of a polyoxyethylene polyoxypropylene alkyl ether.