The alpha-Bi4V2O10 structure was determined from Rietveld analysis of X-ray diffraction powder data and electron diffraction microscopy. alpha-Bi4V2O10 crystallizes in the orthorhombic system, space group Pnma with a 5.4704(2) Angstrom, b = 17.2471(4) Angstrom, and c = 14.9219(4) Angstrom. This compound, derived from the Aurivillius family, presents a typical layered structure of alternating (Bi2O2)(2n) and (VO3)(2n) layers. These layers are built up by corner-sharing VO5 square pyramids in the succession along [010] of three pyramids pointing alternately up and down. Structural relationships between this compound and Bi4V2O10.66 are described, and a structural mechanism that might explain the oxidation at room temperature of alpha-Bi4V2O10 into Bi4V2O10.66 is proposed.