Membrane　distillation　(MD)　has　a　great　potential　in　desalination　and　wastewater　treatment,　but　the　application　of　MD　is　significantly　restricted　by　membrane　scaling.　Membrane　scaling　may　be　affected　by　biopolymers　and　humic　substances,　which　are　ubiquitous　in　aqueous　environment.　However,　the　impact　of　natural　organics,　in　particular　biopolymers,　on　gypsum　scaling　in　MD　is　seldom　investigated.　In　this　work,　the　impact　of　such　organic　compounds　on　gypsum　scaling　were　evaluated　with　synthetic　gypsum　solutions　as　well　as　a　real　desalination　brine.　Model　biopolymers　(i.e.　bovine　serum　albumin　(BSA)　and　sodium　alginate　(SA))　and　model　humic　substances　(humic　acids　(HA)),　were　used　to　investigate　the　effect　of　organics,　and　two　types　of　organics　occurrence　were　considered,　i.e.,　forming　a　layer　on　the　MD　membrane　and　dissolved　in　the　feedwater.　Results　show　that　the　organic　fouling　layer　exhibited　a　very　limited　impact　on　gypsum　scaling　during　MD.　The　dissolved　organics　in　the　feedwater　generally　postponed　rather　than　accelerated　gypsum　scaling　and　membrane　wetting,　particularly　for　BSA　and　HA.　SA　was　less　efficient　in　restricting　gypsum　scaling　due　to　its　higher　carboxyl　content　and　the　stronger　interaction　with　Ca2+.　The　morphological　characterization　showed　that　the　biopolymers　in　the　feedwater　were　able　to　induce　crystal　deformation　and　agglomeration,　forming　irregular　cluster-like　crystals.　Regarding　the　real　desalination　brine,　the　presence　of　BSA　at　50　mg　L–1　apparently　delayed　the　occurrence　of　gypsum　scaling　from　a　concentration　factor　of　2.7–3.2.　As　a　conclusion,　the　impact　of　natural　organics　on　gypsum　scaling　should　be　considered　in　designing　and　operating　MD　for　wastewater　treatment.　©　2020　Elsevier　B.V.