Three new cobalt selenite hydroxo-phosphates laying in the solid solution Co-3(SeO3)(3-x)(PO3OH)(x)(H2O), with x = 0.8, x = 1.0, and x = 1.2 are reported. Single crystals were obtained by hydrothermal synthesis and the crystal structure was determined by single crystal X-ray diffraction. The structure can be described as a 3D framework having selenite and hydroxo-phosphate groups protruding into channels in the crystal structure. Se4+ and P5+ share a split position in the structure so that either SeO3 groups having a stereochemically active lone pair or tetrahedrally coordinated PO3OH groups are present. The OH-group is thus only present when the split position is occupied by P5+. The crystal water is coordinated to a cobalt atom and TG and IR measurements show that the water and hydroxyl groups leave the structure at unusually high temperatures (>450 degrees C). Magnetic susceptibility measurements show antiferromagnetic coupling below 16 K and a magnetic moment of 4.02(3) mu(B) per Co atom was observed.