This paper describes the use of impedance spectroscopy to the study of the stability of supported liquid membranes (SLMs). The advantages of this technique are that it is non-invasive and capable of providing continuous monitoring of SLM stability. This was demonstrated in a series of tests in the phenol transport through SLMs. The technique was also able to identify that the vacated space of the SLM pores was mainly invaded by the strip solution (0.1 M NaOH) during phenol transport.