Water-soluble tantalum complex (NH 4 ) 4 [Ta 2 (C 3 H 4 O 3 ) 4 (O 2 ) 2 O]·3H 2 O was obtained in the powder form, and its crystal structure was solved using single-crystal X-ray diffraction data. Complex anion is composed of two tantalum atoms connected via a bridging oxo group. In addition, each metal is coordinated by two deprotonated lactic acid molecules and by one peroxo group. The determined structure is consistent with13 C NMR, Raman, and IR spectra. This compound can be a potential reagent for advanced solution-based synthesis of tantalum-containing functional materials.