The potential of ratio-spectra derivative spectrophotometry for analyzing mixtures of Penicillin-G sodium and Dihydrostreptomycin sulphate salt, have been demonstrated. Calibration graphs were established up to 30 µg/ml of Penicillin-G and 40 µg/ml of Dihydrostreptomycin. 1^st and 3^rd-derivatives were used. The following working wavelengths were selected: in the 1^st -derivative mode 203-209 nm (peak-to-peak) for Penicillin-G and 235 nm for Dihydrostreptomycin. In the 3^rd-derivative mode 223.6-231 nm (peak-to-peak) for Penicillin-G and 223-235.8 nm (peak-to-peak) for Dihydrostreptomycin. The method was validated. Linearity, limit of detection and quantitation and precision were established for both compounds. The samples were tested for stability in solution and in the course of actual analysis up to 10 hours from their preparation. The method was applied to synthetic mixtures and to the analysis of vials used in veterinary medicine.