The title co-crystal, C6H7NO.C7H5ClO2, belongs to a series of molecular complexes based on the N—O group and was studied in order to establish its possible nonlinear optical behaviour. The 2-picoline N-oxide and 3-chlorobenzoic acid moieties are held together by an intermolecular hydrogen bond between the N—O and O—H groups. This system shows a transparency in the visible region of spectra.