A novel composite film containing metalloporphyrins was fabricated by in situ electrochemical scanning on an L-cysteine self-assembled monolayer modified gold electrode. SEM and ATR-FTIR were used to characterize the structure of the film. The electrochemical properties were investigated through techniques such as a. c. impedance, cyclic voltammetry and chronocoulometry. The porphyrin-L-cysteine film showed no peak in the first cycle, while each of the composite films derived from three different metalloporphyrin-L-cysteines presented a pair of reversible redox peaks in 1.0 mol L-1 H2SO4. These peaks correspond to the rapid redox process of the metal. The supporting electrolyte and its pH value influenced the stability and sensitivity of the composite film. Cupric-porphyrin-L-cysteine film showed good catalytic activity for the reduction of H2O2. The catalytic current was linear to H2O2 concentration in the range 1.0 x 10(-6) to 3.0 x 10(-5) mol L-1, with a correlation coefficient of 0.9995. The detection limit was 1.0 x 10(-7) mol L-1 at a signal to noise ratio of 3. The relative standard deviation was calculated as 2.4% for solutions containing 1.0 x 10(-5) mol L-1 H2O2 (n = 11).