The single crystal needle shape samples of diamagnetically diluted cobalt ludwigite CoMgGaO2BO3 have been grown by the flux method. The results of x-ray diffraction and both dc and ac magnetic measurements are presented. The unit cell volume undergoes a noticable growth under dilution from 328,31 <$E roman A back 35 up 35 symbol Р sup 3> for the parent compound Co3O2BO3 to 345,46 <$E roman A back 35 up 35 symbol Р sup 3> for CoMgGaO2BO3. The temperature of magnetic transition is considerably lower for the latter compound (25 К against 43 К for Co3O2BO3). The dc magnetization temperature dependencies undergo the splitting of field cooled and zero-field cooled regimes and the ac magnetic susceptibility temperature dependencies are frequency dependent pointing out a possible spin-glass freezing in the magnetic system.