A novel amperometric immunosensor based on multi wall carbon nanotubes(MWNTs)/ layer by layer(LBL) assembly of gold nanoparticles and thionine(GNPs-THI)/secretory immunoglobulin A(sIgA)/horseradish peroxidase(HRP) was developed for the detection of salivary secretory immunoglobulin A(sIgA). The layer by layer(LBL) assembly of gold nanoparticles and thionine(GNPs-THI) was assembled through electrostatic adsorption, Au-S and Au-N covalent bonds. Then the salivary anti-sIgA antibody was adsorbed by the formative monolayer of GNPs. Eventually, the horseradish peroxidase (HRP) was used to block the nonspecific adsorption sites on the modified glassy carbon electrode (GCE) and amplify the current signal at the same time. The immunosensor showed a high sensitivity to salivary sIgA with a detection limit(S/N=3) of 15 μg/L.The linear range was 3.0-350.0 μg/L with correlation coefficient(r) of 0.989 7.The response time achieved 95% of the steady state was less than 20 s. Also, the immunosensor had an excellent interference immunity to the interferents of immunoglobulin G (IgG), α amylase and albumin, and the interference rates were -2.13%, -2.85% and -196%,respectively. The antigen-antibody complexes in the measurement were decollemented by 0.1 mol/L of aminoacetic acid. The bioactivities of antigen and antibody were remained well after decollement and the biosensor could be recycled by aminoacetic acid for eight times. Some influence factors on the biosensor were investigated, such as the concentration of substrate and antibody, incubation time, interferents, temperature and pH. It can be used for accurate and fast detection of salivary sIgA to judge the impairment of the mucosal immune system of human owing to its high sensitivity, excellent specificity and convenient detection，and it can be easily regenerated.