It is known that four kinds of MgB2 composite wires have been commercialized. The present study aims to compare the difference of microstructure dependence of mechanical property of those wires. The volume fraction of MgB2 filaments in the wire was designed in the range between 0.1 and 0.19. The voids existing in MgB2 filaments distributed in the scale smaller than a few ten micron meter. The tensile test was carried out at room temperature. Young's modulus, 0.2 % proof stress and strain were

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... termined. The calculated Young's modulus was larger than the observed one for all four different wires. This discrepancy was attributed to the poor sintering of MgB2 filaments as the existence of voids. This situation was proved by the numerically calculated results. A way to realize the higher ductility MgB2 wire was proposed. The proof stress and strain shall be enhanced by replacing to other constituent metallic element with high thermal expansion coefficient and high Young's modulus. The further requirement is to densify MgB2 polycrystalline filaments for reducing the void fraction.