ABSTRACT: The weldability of different sintered materials which consists of Co+Ni and carbon steel has been investigated using C02 laser Autogeneous C02 laser welding were run along the butt between two materials using sets of parameters power and travel speed．In order to study weldability，mechanical tests(bending strength test microhardness test)and metallogical analyses(mierostructure, phase transformation, racture mode)were carried out. The parameters that deeply effect on the bending strength were porosity, energy input and the overlapping of weld metal. To have a sound strength, energy input should have over 0.3kJ/m. Aspect ratio should be over0.9, and porosity should be less than 20 per cent in a weld metal. The microstructure of each parts was shown like this that shank was consisted of tempered mertensite, HAZ shown as martensite. And weld metal had mixed microstructures which were made of austenite and twinned plate martensite.