High strength Ag based alloy tubes with homogeneously dispersed very fine (Mg0.8Ni0.2at%)oxides and (Mg0.5Ni0.2at%)oxides were prepared by internal oxidation. Using the tubes we fabricated high strength Bi-2223 and Bi-2212 multifilamentary tapes with 7 filaments by the powder in tube technique, which have three different arrangements of sheath material such as inner/outer sheaths of Ag alloy/Ag alloy, Ag/Ag alloy and Ag/Ag. For the tapes we examined the microstructures and the critical current IC, especially IC under tensile stress and strain in a self magnetic field at 77K and also usual critical current density JC vs. magnetic field curves at 4.2K. The IC under tensile stress and strain are improved for the high strength sheath tapes, especially those tapes with Ag/Ag alloy arrangement. The JC strongly depends on the inner sheath material, showing high JC for the Ag/Ag and Ag/Ag alloy arrangements. For the tapes with Ag alloy/Ag alloy arrangement some swellings appear in each filament on fabrication and heat-treatment process. Around the swellings observed are some voids and highly mis-aligned grains. This induces the decrease in JC on the connectivity of superconducting grains and also JC under the stress and strain.
