The copper(II)-5-fluorosalicylic acid system was investigated in water and 50 v/v% water-methanol mixture by pH potentiometry combined with UV-vis spectrophotometry, and by the two-dimensional ESR simulation method, respectively. The data revealed that the stable paramagnetic mono- and bis(salicylato) copper(II) complexes [CuLH(-1)] and [CuL2H(-2)](2-) are formed, and at low excess of ligand, the ESR-silent mixed hydroxo complex [Cu2L2H(-3)](-) is also a major species. By the two-dimensional ESR simulation method, the species [CuL]+ in the acidic region, and the minor dimer [Cu2L2H(-2)] were also identified, and the cis and trans isomers of [CuL2H(-2)](2-) were characterized. In frozen solutions, the ESR analysis revealed a slight rhombic distortion of coordination polyhedra for the latter three species.