Four isomeric fluoro-2-formylphenylboronic acids were synthesized and characterized by ¹H, ¹³C, ¹⁹F and ¹⁷O NMR. Molecular and crystal structure of two compounds was determined by single crystal XRD method. pK_a values of all the isomers have been determined by spectrophotometric method and compared with the results for the corresponding benzoxaboroles as well as fluoro- and formylphenylboronic acids. Tautomeric equilibrium with cyclic benzoxaborole form was investigated. The influence of position of fluorine substituents on the properties of investigated compounds is discussed.