Yes, but MP3Gain does not use "peak amplitude" normalization as many "normalizers" do. Audio files with very different peak amplitudes can still sound to the human ear as though they're the same volume.
Instead, MP3Gain uses David Robinson's Replay Gain algorithm to calculate how loud the file actually sounds to a human's ears.
To hear the difference between "maximizing" (peak normalization) and Replay Gain volume normalization,