Human hair is a kind of fibrous keratin which has much cystine residues like wool fiber. It protects human head from the dangerous shock and is an organ to release heavy metals in human body. Recently, in many dyeing field there is a trend to utilize the natural dyes. Cochineal is a reddish natural mordant dye. When the cochineal is applied in human hair dyeing, it is expected that dyeing rate will be slow and wash fastness will be poor on account of large molecular weight relative to oxidative dyes. In this work, we investigated the effects of tributyl phosphate in hair dyeing with natural dye cochineal. Dyeability of hair increased significantly by adding tributyl phosphate in cochineal dyeing. Nevertheless the hair was slightly damaged during dyeing, the dyed hair showed a good wash fastness.