Experimental data are presented and available published information is generalized on phase rela tions in the Bi 2 O 3 -TiO 2 system. The phase diagrams in stable equilibrium and metastable states are con structed. The homogeneity range of the phase with a sillenite Bi 12 TiO 20 structure is refined, and so is the tem perature range of the existence of the metastable and equilibrium states of the phase with a pyrochlore Bi 2 Ti 2 O 7 structure.