A new erasable(decolorable) ink has been developed for paper recycling and reuse. The erasable ink can be easily decolored in two ways; a heat treatment and a solvent treatment. It is composed of three components; leuco dye, developer and erasing reagent. The leuco dye is originally colorless, but it acquires color with developer. The developer is a phenolic compound. The erasing reagent absorbs the developer, and thus, the dye is not developed. It is easily understood as reverse of thermal sensitive recording paper(thermal paper) process. The erasable ink is originally colored by a bond between the dye and the developer, heat treatment or solvent treatment breaks the bond, and the developer bonds with the erasing reagent. Thus the printed image is stably decolored. One of the principal advantages of this erasable ink is that a huge volume of paper can be decolored using the two methods. The various possible applications of the erasable ink include erasable toner, erasable ink ribbon, erasable crayon and erasable liquid ink. Therefore, this ink has the potential to realize an efficient, cost-effective paper recycling and reuse system.