Silver-europium double sulfate AgEu(SO4)(2) was obtained by solid-phase reaction between Ag2SO4 and Eu-2(SO4)(3). The crystal structure of AgEu(SO4)(2) was determined by Monte Carlo method with simulated annealing, and after that, it was refined by the Rietveld method from X-ray powder diffraction data. The compound crystallizes in the triclinic symmetry, space group P (1) over bar ( a = 0.632929(4), b = 0.690705(4), c = 0.705467(4) nm, alpha = 98.9614(4), beta = 84.5501(4), gamma = 88.8201(4)degrees, V = 0.303069(3) nm(3)). Two types of sulfate tetrahedra were found in the structure, which significantly affects the spectroscopic properties in the IR-range. In the temperature range of 143-703 K, the average linear thermal expansion coefficients of cell parameters a, b, and c are very similar, (1.11-1.67) x 10(-5) K-1 in magnitude, and therefore, AgEu(SO4)(2) expands almost isotropically. Upon heating in argon flow, AgEu(SO4)(2) is stable up to 1053 K. The luminescence spectra in the region of ultranarrow D-5(0)-F-7(0) transition contain a single narrow and symmetric line at 579.5 nm that is evidence of good crystalline quality of AgEu(SO4)(2) and uniform local environment of Eu3+ ions in the structure. Distribution of luminescence bands is determined by the environment of Eu3+ ions in the structure. Influence of Ag+ ions on the electron density distribution at Eu sites is detected.