Complete solid solubility is found in the pseudobinary system Ba2TiGe2O8-Ba2TiSi2O8 by making studies on ceramics and single crystals (Czochralski technique). The spontaneous birefringence perpendicular to the polar axis of the orthorhombic low temperature phase was measured vs. temperature and Si contents: the temperature of the phase transition of species 4mmFmm2 is of 2nd order and decreases from 1103 K at 0 at.% Si to about 400 K at 40 at.% Si. The pyroelectric coefficient in the orthorhombic mm2 and the tetragonal 4mm phases is of the order of 10-6 C m-2 K-1 in the entire system and all compositions studied have a positive temperature coefficient except Ba2TiGe2O8, in which the pyroelectric coefficient changes sign at .apprx. 308 K. The proposed space group of the orthorhombic phase is C2v11-Cmm2.