The paper presents the results of mechanical bend testing of tin doped bismuth microwire in glass isolation with internal diameters (1.5 – 15) μm and external (10 – 60) μm. The impurity of tin in quantity 0.01, 0.05 and 0.075 atomic percentage was introduced in initial ingots in the process of material synthesis. The criterion of estimation of mechanical bend testing of the microwire, as the measure of their flexibility, is the value of critical bending radius (rcr) and the bend was carried out up to rupture. It was established, that reduction of both internal and external diameters of tin doped bismuth microwire conducts to reduction of the critical bending radius, i.e. to the growth of their flexibility for all investigated concentration of tin. It is necessary to note, that tin doped bismuth microwire are much more elastically in comparison with microwire crystals from pure bismuth. It was established, that for some bismuth microwire doped by 0.01 аt % of tin and internal diameters d ≤ 3 μm samples were not broken off even in case of achievement of critical bending radius. This possibly, is connected with the presence of plastic deformation of investigated samples. The received results of bend testing show that tin doped bismuth microwire crystals possess high flexibility, that give the possibility of their practical use as sensitive tiny elements of strain gauges.