Cylindrical rod-like specimens with various diameters for Zr65Cu27.5Al7.5 alloy were prepared by arc-melting and Cu-mold casting under different hydrostatic pressures. The influences of hydrostatic pressure on the alloy’s glass-forming ability (GFA) and mechanical properties were investigated. Results show that the alloy’s GFA presents sensitive response to the variation of hydrostatic pressure at kPa level, and lower or higher pressures can decrease the GFA. The sensitive hydrostatic pressure dependence of GFA is related with the microstructures of primary phases.