It　is　revealed　by　recent　experimental　and　theoretical　nanoindentation　studies　that　the　low　concentration　of　monovacancy　produces　an　abnormal　noticeable　stiffening　effect　on　graphene　sheets,　which　depending　on　the　defect　type.　As　for　graphene-like　quasi-two　dimensional　(2D)　nanomaterials,　the　single-layer　molybdenum　disulfide　(SLMoS2)　has　intrinsic　structural　defects　that　are　distinct　to　graphene.　Therefore,　it　is　intriguing　to　investigate　if　any　kind　of　defects　will　lead　to　such　unique　effect　on　the　mechanical　properties　of　SLMoS2,　including　the　elasticity　and　strength.　Following　our　preliminary　studies　on　the　VMoS3　point　defect,　herein,　we　perform　molecular　dynamics　simulations　to　look　into　the　effect　of　the　low　concentration　of　single　molybdenum　vacancy　defects　on　the　mechanical　properties　of　SLMoS2,　under　uniaxial　tensile　tests.　The　defect　fractions　of　the　single　Mo　vacancy　varying　from　0.1%　to　1.0%　are　considered　in　our　works,　together　with　the　random　and　regular　vacancy　distributions.　Single　molybdenum　vacancy　defects　are　found,　as　common　intuition　would　suggest,　to　reduce　the　mechanical　properties　of　SLMoS2,　including　the　elastic　modulus　and　tensile　strength.　The　effect　of　chirality　on　the　mechanical　properties　of　the　SLMoS2　is　also　discussed　in　the　present　work.　©　2017　IEEE.