Landfill　leachate　(LFL),　which　contains　organic　and　inorganic　contaminants　in　high　concentration,　poses　a　detrimental　hazard　to　the　ambient　environment.　Although　membrane　distillation　(MD)　shows　great　potential　in　wastewater　treatment,　the　membrane　fouling　in　LFL　treatment　is　still　a　rarely　reported.　In　this　study,　the　membrane　fouling　was　systematically　investigated　in　a　real　LFL　treatment　by　a　direct　contact　MD　system.　Various　characterization　methods,　such　as　scanning　electron　microscopy,　scanning　electron　microscopy　with　energy-dispersive　X-ray　spectroscopy,　and　attenuated　total　reflection　Fourier　transform　infrared　spectroscopy　were　adopted　in　membrane　fouling　identification.　Increasing　membrane　fouling　was　observed　with　the　increasing　feed　pH.　The　analysis　of　membrane　autopsy　and　differential　log-transformed　absorbance　spectroscopy　revealed　that　the　increase　of　feed　pH　strengthened　the　deprotonation　of　carboxyl　groups　in　organic　matter,　contributing　to　the　formation　of　organo-inorganic　complexation.　The　interaction　between　magnesium-related　substances　and　humic-like　matter　might　be　the　culprit　of　organo-inorganic　membrane　fouling　in　alkaline　feed　condition　based　on　correlation　analysis　(R-2　=　0.996).　The　results　enhance　the　understanding　of　the　mechanisms　by　which　pH　affects　membrane　fouling　and　lay　the　foundation　for　controlling　membrane　fouling　in　the　LFL　treatment.