We propose a third-order intermodulation distortion (IMD3) compensation scheme based on the bidirectional modulation of 2-Ch phase modulator (PM). We realize the destructive combination of IMD3 by using different modulation efficiencies and appropriately adjusting the input optical power ratio to satisfy a fixed relationship with modulation efficiency. The primary advantage of this scheme is that out-of-phase IMD3 is introduced using only one 2-Ch PM, thereby resulting in the cancellation of IMD3. Up to 27-dB suppression in IMD3 is experimentally demonstrated—a feature that will be useful in low-distortion analog optical transmission.