This study was performed to investigate the inhibitory activity of ethanol extract from Ecklonia cava (EE-EC) against trypsin and the stability of this activity under various heat and pH conditions. As a results, The EE-EC showed trypsin inhibitory activity of 77, 54, and 32% at concentrations of 5, 2.5, and 1 mg/mL and was not affected by the heat treatment conditions used in this study. Whereas trypsin inhibitory activity of EE-EC was stable in the pH range of 2-8, but decreased with pH treatment of pH 10 compared with the control. Therefore, the EE-EC could be useful as a natural and functional agent.