The aim of this work is to compare between erasable and disappearing inks and study their role in the forgery of different documents. The obtained results showed differences between erasable and disappearing inks that help the documents examiner to deal with them when submitted in cases. The disappearing ink which contains phenolphthalein loses its color by time faster than that contains thymolphthalein. While the color of erasable ink did not generally change by time at room temperature but changed on exposure to UV light. On the other hand, the disappearing ink is absorbed by paper while erasable ink remains on paper surface. The two types of ink are more stable on polycarbonate polymer sheets. The polymer component of erasable ink is chemically bonded with polycarbonate polymer leading to ink stability. The presence of Ti in the pigment of disappearing ink acts as tag in forgery examination due to its diffusion inside polycarbonate sheet.