The　instability　of　supported　liquid　membranes　(SLMs)　for　use　in　copper　(II)　ion　extraction　was　investigated　in　this　paper.　The　degradation　behavior　of　these　SLMs　was　monitored　in　situ　by　electrochemical　impedance　spectroscopy　(EIS).　The　electrical　properties　of　a　SLM　cell　can　be　described　by　an　equivalent　circuit,　Rs(CmRm)Q.　The　model　parameters,　membrane　resistance　(Rm)　and　membrane　capacitance　(Cm)　can　be　used　to　characterize　the　degradation　behavior　of　SLMs.　Experimental　data　for　Rm　and　Cm　indicated　that　the　loss　of　membrane　liquid　(ML)　during　the　mass　transfer　process　consists　of　three　stages.　Results　also　suggest　that　emulsion　formation　was　the　dominant　instability　mechanism　for　these　SLMs.　The　solubility　and　osmotic　pressure　were　also　shown　to　not　be　major　factors　contributing　to　the　instability　although　both　contributed　to　the　loss　of　the　liquid　membrane.　The　pore　size　of　the　polymeric　support　increased　during　the　first　run　but　remained　almost　constant　in　subsequent　runs.　©　2009　Elsevier　B.V.　All　rights　reserved.