The glasses with (25-x)La₂O₃·xGd₂O₃·25B₂O₃·50GeO₂ composition corresponding to the (La,Gd)BGeO₅ were prepared, and the substitution effect of gadolinium ions (Gd³⁺) on crystallization behavior and phase formation was examined by DTA, XRD and Raman techniques in detail. Ferroelectric (La,Gd)BGeO₅ phase with hexagonal stillwellite structure were crystallized in the composition range of x = 0-15. Although no significant change in physical properties was observed in the whole composition range, crystallization behavior was drastically changed as the progressive substitution of Gd³⁺ was carried out (i.e., crystallization of monoclinic phase of (La,Gd)BGeO₅ and high-pressure phase of Gd₂Ge₂O₇ with a triclinic structure). Structure of the glasses and crystallized phases, and the phase formation mechanism were also discussed.