A series of novel self-dispreading phenoxy carboxylic acid derivatives were designed and synthesized by I2 catalyzed one-step reaction. Their structures were confirmed by IR, NMR, and HRMS. The derivatives can self-spread and float on the water surface. Preliminary bioassays showed that some compounds, 3i–3p, had excellent herbicidal activities against water hyacinth. This strategy provided a novel approach for the water hyacinth control.