We present a simple method for measuring Henry's constant k(H) of ethanol using photoacoustic spectroscopy. At T = 298.1 K the measured value for k(H) is (0.877 +/- 0.039) kPa (.) ka (.) mol(-1). Our data show that Henry's law is valid at ethanol Molalities between 0.1 mol (.) kg(-1) and 1.4 mol (.) kg(-1). The temperature dependence of Henry's constant was carefully examined by measuring the ethanol vapour pressure of six different aqueous solutions between T = 273.1 K and T = 298.1 K. By analysing the gas phase concentration and applying Henry's law, an ethanol molality of 0.864 mol (.) kg(-1) in the liquid phase can be measured with an error of +/-0.038 mol (.) kg(-1). The detection limit of the photoacoustic sensor is a gaseous-ethanol pressure of 10(-3) kPa. Ethanol molality changes as low as 1.10(-3) mol (.) kg(-1) can be measured.