Despite　graphene　is　considered　to　be　a　promising　application　material　in　many　fields　due　to　its　unique　optical,　electrical,　and　mechanical　properties.　However,　the　releasing　of　graphene　into　the　sludge　system　after　its　industrial　application　is　concerned　since　the　toxicity　of　graphene　to　the　ecosystem　is　still　unclear.　The　objective　of　this　study　was　to　investigate　the　effect　of　graphene　on　the　growth　of　Acidithiobacillus　ferrooxidans　(A.　f)　at　1,　10　and　50　mg·L-1　of　graphene.　The　results　showed　that　the　decreasing　in　concentrations　of　graphene　markedly　inhibited　the　growth　of　A.　f.　and　hence　the　toxicity　increased.　For　example,　the　OD420　was　0.045　at　1　mg·L-1　of　graphene　after　48　hours　incubation　compared　to　the　control　of　0.163.　Similarly,　1.546　mg·L-1　of　soluble　protein　of　the　culture　at　1　mg·L-1　of　graphene　was　observed,　which　was　much　lower　than　control　(3.789　mg·L-1).　In　addition,　1　mg·L-1　of　graphene　significantly　inhibited　the　pH　and　oxidation-reduction　potential　(ORP)　of　A.　f..　Furthermore,　scanning　electron　microscopy　(SEM)　confirmed　that　a　low　graphene　concentration　caused　cell　membrane　disruption,　while　high　graphene　concentration　slightly　impacted　on　A.　f.　The　fluorescence　microscope　showed　that　no　live　cell　was　detected　at　graphene　concentration　of　1　mg·L-1.　The　new　finding　in　this　study　provided　a　new　insight　into　dose-dependent　and　the　interaction　between　the　cells　and　graphene＇s　extremely　sharp　edges.　©,　2015,　Science　Press.　All　right　reserved.