A novel surfactant having an azulene moiety, sodium 3-decyl-l-azulenesulfonate (C10AS), has been synthesized. The surface-activity of C10AS is lower than that of its structural isomer, sodium 4-decyl-l-naphthalenesulfonate (C10NS), probably caused by the higher hydrophilicity of C10AS due to the dipole moment of azulene moiety. C10AS exhibits the higher antipeptic activity than the propyl derivative (C3AS) below its critical micelle concentration.