The　ductile　fracture　of　structural　steel　including　weldment　can　be　described　as　a　progressive　process　with　void　nucleation,　growth　and　coalescence.　The　effects　of　mechanical　heterogeneity　of　the　weldment　were　investigated　experimentally　on　the　ductile　fracture　behaviors　of　the　base　metal　and　the　weld　metal　using　round-bar　tensile　notched　bars.　The　results　show　that　the　mechanical　heterogeneity　of　weldment　has　certain　effects　on　fracture　strain,　stress　triaxiality　at　fracture,　critical　void　growth　and　the　material　constant　C.　The　smaller　the　distance　between　the　notch　root　and　the　fusion　line,　the　larger　the　fracture　stain,　the　smaller　the　stress　triaxiality　and　the　larger　the　critical　void　growth　rate.　(C)　1998　Elsevier　Science　Ltd.　All　rights　reserved.