Abstract: Samples of pretreated serum from human-body's vein were analysed by field desorption mass spectrometry (FDMS). The molecular weight distribution of mixing amino acids and peptides from serum was obtianed. The experimental results showed when acid concentration in serum sample was increased and hydrolysis time was prolonged that the bar graphs form of a spectrum were moved to small masses, on the contrary, to large masses. The most six peptides were got. Parts of possible component of amino acids into correspondence with mass numbers were kisted. Furthermore, serum which was added ethanol or methanol was determined, and the experimental results were explained initially.