As a precursor of highTcsuperconductors, glasses in the system BixCaSrCu2Ow(x=1.5,2.7) have been prepared using twin‐roller and metal‐plate quenching procedures. Transition range viscosities have been measured on samples as thin as 0.02 mm using the beam‐bending method with a technical modification. From the viscosity data, the system Bi‐Ca‐Sr‐Cu‐O can be characterized as a ‘‘fragile’’ liquid like the ZrF4‐based fluorides. The possibility of drawing fibers of highTcsuperconductor precursors is discussed on the basis of the temperature dependence of viscosity.