Gain band expansion of a Raman amplifier based on a Raman fiber oscillator (RFO) was tested with two Raman lasers, which yielded a broad gain spectrum of about 40 nm. However, they also introduced gain-clamping behavior in the short-wavelength range and abnormal excessive gain in long-wavelength channels, which were undesirable for practical application. The proper mechanism of the behavior was analyzed and experimentally demonstrated to apply to a gain-clamped (GC) amplifier based on a RFO. Appropriate configuration of the GC-RFO for wide gain bandwidth was proposed and characterized.