In this paper, the tensile testing method at the intermediate strain rate is established and tensile tests of steel sheets for an auto-body have been performed to evaluate dynamic material properties. A high speed tensile testing machine has been developed for tensile tests at the intermediate strain rate. A simple jig fixture for gripping a specimen has been designed to diminish the load ringing phenomenon induced by unstable stress propagation at the high strain rate. Design of the specimen has to be performed for the dynamic tensile test considering the inertia and wave propagation effect. Finite element simulations are carried out to investigate the geometric effect of a specimen such as the parallel region, the width and the fillet radius. Optimum dimensions of a specimen are determined from the analysis and experiment. The optimum specimen together with the dynamic tensile test machine with the special jig fixture provides an accurate stressstrain curve with negligible load ringing phenomenon.