Two new manganese() selenites with the formula Mn4(H2O)3(SeO3)4 (1) and Mn3(H2O)(SeO3)3 (2) have been synthesized by using mild hydrothermal conditions under autogeneous pressure. The crystal structure of both compounds has been solved from single crystal X-ray data. The structures consist of a three-dimensional framework formed by MnO6 octahedra and (SeO3)2 selenite anions with trigonal pyramidal geometry. Compound 1 shows the existence of sheets constructed from zig-zag chains linked to MnO6 octahedra. Compound 2 exhibits zig-zag chains formed by edge-sharing dimeric octahedra which are interconnected by Mn2O10 octahedra. The IR and Raman spectra show the characteristic bands of the selenite anion. Studies of luminescence at 6.0 K and diffuse reflectance spectroscopy have been carried out for both compounds. The Dq and Racah parameters are Dq = 715, B = 705 and C = 3420 cm 1 for 1 and Dq = 710, B = 700 and C = 3425 cm 1 for 2. The ESR spectra are isotropic with a g-value of 2.00(1), which remains unchanged with variation in temperature. Magnetic measurements indicate the presence of antiferromagnetic interactions in both phases.