Abstract: To study the tensile stress-strain relation and the failure mechanism of two stainless steel types (duplex grade S22053 and austenitic grade S30408 stainless steel made in China) and the corresponding weld metals, tensile tests were conducted on four groups of test specimens including three duplicate specimens in each. The fracture micro-mechanism was analyzed by using the scanning electron microscopy (SEM) on the fracture surfaces of the specimens. Based on the experimental stress-strain curves, the parameters of the material constitutive models were obtained by curve-fitting using the modified Ramberg-Osgood equations. Comparisons of the tensile stress-strain relation were made between the base metal and weld metal. The results indicated that both base metal and weld metal fractured in a ductile manner, and their stress-strain relations exhibited significant nonlinearity. Compared with the base metal, the weld metal had a higher yield strength and ultimate tensile strength, but lower ductility. The stress-strain relations of the base metal and the weld metal obtained in the tests can be well fitted by the modified Ramberg-Osgood equations. The differences of stress-strain relation between base metal and weld metal should be taken into consideration, and the corresponding constitutive model should be used separately in the accurate load capacity analysis of welded stainless steel connections.