The temperature behaviour of 0.955 AgNbO3-0.045 LiTaO3 and AgNbO3 ceramics was studied in the range from 10 to 415 K using Raman spectroscopy. Ab initio calculations of the Raman spectra in the Pmc21 phase of AgNbO3 were carried out using three potentials (A-PZ, PBE, and PBEsol) for spectral interpretation. The peculiarities in the Raman spectra in AgNbO3 ceramics are observed and explained. The differences in the spectra of the 0.955 AgNbO3-0.045 LiTaO3 and AgNbO3 ceramics are shown. The temperatures of the structural changes in the 0.955 AgNbO3-0.45 LiTaO3 and AgNbO3 ceramics were discussed. A structural phase transition below 120 K was observed in silver niobate. A phase transition was observed at 310 K and below 150 K in 0.955 AgNbO3-0.045 LiTaO3.