The 2.5th order differential polarographic reduction behavior of malonaldehyde (MLD) was studied. A sensitive measurement method of the determination of MLD for biological samples was given by using differential voltammetry with a static mercury drop electrode at a scanning speed of 80mV/s in a solution of 0.1mol/L NH4Cl. The linear response range of current(e″) against the concentration of MLD was 1.0×10−6to 1.0×10−3mol L and the detection limit was 1.0 × 10−7mol/L. The contents of MLD in the sample of cardiac myocytes was determined rapidly and simply by means of the method.