Microplatelets of the layered-kagome compound BaCo3(VO4)2(OH)2, which is the Co2+ analogue of mineral vesignieite BaCu3(VO4)2(OH)2, have been prepared with very high yield by hydrothermal reaction using synthetic karpenkoite Co3V2O7(OH)2·2H2O as starting reagent. The Rietveld refinement of X-ray diffraction data indicates that Co3V2O7(OH)2·2H2O is isostructural with martyite Zn3V2O7(OH)2·2H2O. Two single-phased samples of microstructured BaCo3(VO4)2(OH)2 have been characterized using powder X-ray diffraction, FT-IR and Raman spectroscopies, thermal analyses, scanning electron microscopy, energy-dispersive X-ray spectroscopy and magnetisation measurements. Their crystallite sizes perpendicular to the c-axis are in the range of 92(3) to 146(6) nm and depend on the synthesis conditions. Results have been compared to those previously obtained for quasi-spherical nanoparticles having a crystallite size of the order of 20 nm, to explore the effect of the crystallite size on the properties of BaCo3(VO4)2(OH)2. This study highlights that the magnetic properties depend on the crystallite sizes only at low temperatures.