Abstract: The structures of dye 3,3'-bis(1-n-octyl-2-methylindol-3-yl) phthalide(ck-16) in coloring and decoloring states were analyzed by ¹³C NMR. The chromogenic properties of ck-16 interacted with different color developers in ethyl alcohol were studied by UV-visible spectroscopy. The composition ratio and instability constant of the complexes composed of ck-16 and the color developers were measured. Furthermore,the effect of external conditions on the absorbance at λ_max of the system was investigated. ¹³C NMR results show that the delocalized bonds formed between electron donor(N) and acceptor(O) atoms lead to ring cleavage of the phthalide to a carboxylate as a colored form. The chromogenic properties of ck-16 vary with different color developers. When the molar ratio of ck-16 to four color developers(FeCl₃,oxalic acid,CuCl₂ and salicylic acid) are all 1:1,the combination between ck-16 with Fe³⁺ is the most stable,followed by oxalic acid and Cu²⁺. Among the four color developers,the combination between ck-16 with salicylic acid is the most instable. The time has little influence on the absorbance at λ_max of ck-16/FeCl₃ and ck-16/H₂C₂O₄.However,different sensibility is observed when water is added. The ck-16/FeCl₃ fades more rapidly with water than ck-16/H₂C₂O₄,and exhibits potential application as water sensitive recording or copying materials.