The structure of Co2.5VMoO8 was refined by the Rietveld method. The lattice constants are: a = 0.50453 nm; b = 1.03448 nm; c = 1.73925 nm, space group Pnma. The crystal structure of the compound is isotypic with Mg2.5VMoO8. The structure is a framework of MoO4 and VO4 tetrahedra with linking octahedral and trigonal prismatic CoO6 groups. Co2.5VMoO8 melts incongruently at 1080 +/- 5degreesC depositing solid CoMoO4. (C) 2003 Kluwer Academic Publishers.