An amphiphilic diperoxide, palmitoyl (3-carboxy propionyl) sebacoyl diperoxide (PSD), was synthesised by the successive condensations of sebacoyl chloride with peroxypalmitic acid and monoperoxysuccinic acid in a pyridine medium and further characterised by i.r., H-1 n.m.r., MS as well as elemental analysis. The amphiphilic character of the diperoxide as surfactant was confirmed by the fact that the average area occupied by per PSD molecule at the air-water interface was found to be 0.31 nm(2) by the LB film method. The activation energy of the diperoxide for decomposition was determined by d.s.c. and calculated to be 142.7 kJ/mol.