The galactic cosmic rays induced ionosphere of Titan is studied from 0 to 70 km. We resent here a new model developed for calculating the concentration of cations, anions, and electrons depending on the mixing ratio of electrophilic species present in the atmosphere of Titan. The existence of neutral species in which electrons can be attached by the three-body process produces anions and, depending on the abundance of electrophilic specie, reduces, even very strongly, the concentration of electrons. We also discuss the effect of the electron detachment of negative ions by absorption of solar radiation, which could produce a decrease in the anions density and, consequently, an increase in the electron density. ¿ 2000 American Geophysical Union