The relationships among macro-bending loss, power of the 1500-nm amplified spontaneous emission (ASE), gain, and noise figure of an erbium-gallium co-doped silica fiber amplifier are investigated and explained. The dependence of macro-bending loss on different bending radii is examined. Using different fiber lengths and bending radii, the effects of macro-bending on ASE, gain, and noise figure are analyzed in comparison to an unbent fiber. The ASE power changes because macro-bending alters the number of Er3+ ions in the 4I13/2 level that decay to the 4I15/2 level emitting photons of shorter and longer wavelengths. The trade-off relationship that exists between the change in the ASE power and signal loss, where both result from macro-bending, explains the gain change. Fiber length also affects the changes in the ASE power and gain. Noise figure in the longer-wavelength region increases. In the shorter-wavelength region, for a long fiber, the noise figure improves only slightly. For a short fiber, it worsens due to gain decrement. The findings from this study explain the reason for gain improvement upon suppressing either a competing or a noncompeting ASE via filters or macro-bending in other rare-earth-doped fibers.