We demonstrate a strained Si0.91Ge0.09-based carrier-injection Mach-Zehnder (MZ) optical modulator using the enhanced plasma dispersion effect in strained SiGe through mass modulation for the first time. The SiGe modulator has an injection current of 1.47 mA for a phase shift of π which is lower than that for a Si modulator. Also, it is expected that the injection current can be further reduced by increasing the strain and Ge fraction, enabling operation at an injection current of less than 1 mA. As an example of the dynamic characteristics, 10 Gbps modulation with clear eye opening was obtained by the pre-emphasis method.