Mixed alkali bismuth borate glasses of composition xLi2O–(30− x) K2O–10 Bi2O3–55 B2O3:5 V2O5 (LK-series) were prepared by melt quench technique. The amorphous nature of these samples was confirmed from their X-ray diffraction. The density of the samples was measured using Archimedes principle and the molar volumes were determined from the density data. The glass transition temperature of the samples was found to vary non-linearly with the Li2O content (x). The spectroscopic properties of glass samples were studied using infrared (IR) and Raman spectroscopic techniques. IR measurements indicate that the network structure of the studied glasses is based on the BiO3 pyramidal and BiO6 octahedral units and also on BO3 and BO4 units. Raman spectra of these alkali combinations with V2O5 present drastic changes in the intensity of various Raman bands. The observation of disappearance and reappearance of some IR and Raman bands and non-linear variation of the peak positions of some of these bands with x is an important result pertaining to the mixed alkali effect in this glass system. Acting as complimentary spectroscopic techniques, both types of measurements IR and Raman revealed that the network structure of the studied glasses is mainly based on BO3 and BO4 units placed in different structural groups, BO3 units being dominant and bismuth exists as BiO3 and BiO6 octahedral units.