Single crystals of Co3O2BO3 with partial (4%) substitution of Co by Cu ions were synthesized by the flux technique. X-ray diffraction and magnetic studies were carried out. The x-ray diffraction measurements show clearly that Cu preferentially occupies only one of the four nonequivalent crystallographic positions, the one with the smallest electric field gradient. The ferrimagnetic ordering near TN = 43 K and the high magnetic hardness in this magnetic phase are similar to those of Co3O2BO3. Copper substitution causes a small reduction in the effective magnetic moment.