A series of tetracoordinate mononuclear Co(II) complexes [Co(L1)2(X)2] (1-3) and [Co(L2)2(X)2] (4-6) {where L1 = 2-amino-1-methyl-benzimidazole; L2 = 4-methylquinoline; X = Cl, Br, I} have been synthesized and studied in detail. Compounds were characterized by spectroscopic methods along with their molecule structure determined by the single-crystal X-ray diffraction. All complexes have been investigated in the static magnetic field Bdc = 0.1 T using SQUID magnetometry. DC magnetic data were fitted by a spin Hamiltonian model appropriate to a zero-field splitting system. The axial zero-field splitting parameters D ranged as-14.44 (1),-13.05 (2),-7.50 (3),-6.76 (4), +7.19 (5),-5.58 (6) cm-1. The experimental zero-field splitting parameters are compared with those ob-tained by ab initio calculations of the CASSCF + NEVPT2 + SOC quality.