||The synthesis, structural characterization, and magnetic properties of La3Co2SbO9 double perovskite are reported. The crystal structure has been refined by X-ray and neutron powder diffraction data in the monoclinic space group P21/n. Co2+ and Sb5+ have the maximum order allowed for the La3Co2SbO9 stoichiometry. Rietveld refinements of powder neutron diffraction data show that at room temperature the cell parameters are a=5.6274(2) Ã…, b=5.6842(2) Ã…, c=7.9748(2) Ã… and Î²=89.999(3)Â°. Magnetization measurements indicate the presence of ferromagnetic correlations with TC=55 K attributed to the exchange interactions for non-linear Co2+â€“Oâ€“Sb5+â€“Oâ€“Co2+ paths. The effective magnetic moment obtained experimentally is Î¼exp=4.38 Î¼B (per mol Co2+), between the theoretical one for spin only (3.87 Î¼B) and spin-orbit value (6.63 Î¼B), indicating partially unquenched contribution. The low magnetization value at high magnetic field and low temperature (1 Î¼B/f.u., 5 T and 5 K) and the difference between ZFC and FC magnetization curves (at 5 kOe) indicate that the ferromagnetism do not reach a long range order and that the material has an important magnetic frustration.