La2Ti2SiO9 has been synthesized by chemical transport reaction using the system LaOCl and TiO2 in a temperature gradient; the silicium atoms came from the silica tube. Its structure was determined and refined down to R = 0.021 for 1041 observations and 77 variables. The octahedral titanium atoms and the tetrahedral silicium atoms lead to layers parallel to the (100) plane, the lanthanum atoms connecting these layers. The structural feature of this phase are compared to the one of La4Ti9Si4O30 previously reported.