Abstract The results of an investigation of the structure of Co 2+ ions in x LiF-(100− x )B 2 O 3 and x K 2 SO 4 -(100− x )ZnSO 4 glasses with 10 ≤ x ≤ 50 mol% using electron spin resonance spectroscopy (ESR) and optical absorption techniques are reported. The ESR spectra of Co 2+ doped LiFB 2 O 3 glasses at 4.2 K has a broad asymmetric line at g = 4.41 ± 0.02 and a broad hump at g = 2.30 ± 0.05. ESR spectra of Co 2+ ions in K 2 SO 4 ZnSO 4 glasses at 4.2 K have a single broad symmetric line at g = 4.38 ± 0.02. Optical absorption spectra were recorded at room temperature. The observed bands were interpreted in terms of ligand field theory. From the spectral analysis the crystal field parameter ( Dq ) and the Racah interelectronic repulsion parameters ( B and C ) have been evaluated. By correlating the ESR and optical absorption data, the covalency parameter has been evaluated.