This paper presents our work for the measurement of the complex permittivity of liquids, carried out in the framework of a European Metrology research project entitled “Traceable measurement of field strength and SAR for the Physical Agents Directive”. One of he aims of this project was to establish the traceability of the specific absorption rate measurements to the SI up to 10 GHz. We use a vector network analyser to measure the S21 parameter of coaxial cells containing the liquid under test (a reference liquid or an equivalent tissue liquid). The method does not require the network analyser to be calibrated in terms of impedance. In fact, only the length of the coaxial cell and the working frequency need to be known.