A flow-through optical absorption detector for HPLC was constructed using a novel deep-UV light-emitting diode as radiation source with a peak emission wavelength of 255 nm. For measuring the transmitted intensity (a property correlated to Transmittance) a special UV-sensitive photodiode was employed. Besides the power source, no optical or electronic components other than an inexpensive operational amplifier and a few passive components were necessary. The performance of the detector was tested with three substances, namely nitrobenzene, benzoic acid and methyl benzoate, which were separated by gradient elution using an acetonitrile/water mixture and tetrabutylammonium hydrogensulfate as pH-buffer. Calibration curves for concentrations between 1.6 µg·mL⁻¹ and 400 µg·mL⁻¹ (nitrobenzene) and 8 µg·mL⁻¹ and 2.5 mg·mL⁻¹ (benzoic acid and methyl benzoate) were determined and coefficients of determination, r², of 0.9945, 0.9972 and 0.9996 were obtained for quadratic curve fits for the 3 compounds respectively. Relative standard deviations (n = 7) for peak areas were determined as 0.35% (nitrobenzene, 80 µg·mL⁻¹), 0.27% (benzoic acid, 400 µg·mL⁻¹) and 0.83% (methyl benzoate, 200 µg·mL⁻¹). The lower limits of detection were found to be 750 ng·mL⁻¹, 5.8 µg·mL⁻¹ and 12 µg·mL⁻¹ for nitrobenzene, benzoic acid and methyl benzoate respectively.