Structural　defects　in　monolayer　molybdenum　disulfide　(MoS2)　have　significant　influence　on　the　electric,　optical,　thermal,　chemical,　and　mechanical　properties　of　the　material.　Among　all　the　types　of　structural　defects　of　the　chemical　vapor　phase-grown　monolayer　MoS2,　the　VMoS3　point　defect　(a　vacancy　complex　of　Mo　and　three　nearby　S　atoms)　is　another　type　of　defect　preferentially　generated　by　the　extended　electron　irradiation.　Here,　using　the　classical　molecular　dynamics　simulation　with　reactive　empirical　bond-order　(REBO)　potential,　we　first　investigate　the　effect　of　VMoS3　point　defects　on　the　elastic　properties　of　monolayer　MoS2　sheets.　Under　the　constrained　uniaxial　tensile　test,　the　elastic　properties　of　monolayer　MoS2　sheets　containing　VMoS3　vacancies　with　defect　fraction　varying　from　0.01　to　0.1　are　obtained　based　on　the　plane　anisotropic　constitutive　relations　of　the　material.　It　is　found　that　the　increase　of　VMoS3　vacancy　concentration　leads　to　the　noticeable　decrease　in　the　elastic　modulus　but　has　a　slight　effect　on　Poisson’s　ratio.　The　maximum　decrease　of　the　elastic　modulus　is　up　to　25 %.　Increasing　the　ambient　temperature　from　10 K　to　500 K　has　trivial　influences　on　the　elastic　modulus　and　Poisson’s　ratio　for　the　monolayer　MoS2　without　defect　and　with　5 %　VMoS3　vacancies.　However,　an　anomalous　parabolic　relationship　between　the　elastic　modulus　and　the　temperature　is　found　in　the　monolayer　MoS2　containing　0.1 %　VMoS3　vacancy,　bringing　a　crucial　and　fundamental　issue　to　the　application　of　monolayer　MoS2　with　defects.　©　2016,　Li　et　al.