Abstract: The paper describes an improved thermodynamic method for measurements of characterizing acoustic nonlinearity parameter B/A of liquids and biological media.The method is based on measurement of small variation of sound speed with static pressure in an adia-batic process.Phase-comparative technique is applied in order to get high sensitivity.only about one Atm.static pressure is needed,the measurements are much easier to carry out than traditional techniques previously used.Results from measurements of distilled water,polyethylene glycol and so on show that the method is practical and the apparatus works quite well.The accuracy of measurements is within 5%.