A highly sensitive sandwich enzyme-linked immunosorbent assay (ELISA) for quantifying BSA was established, based on two mAbs that recognize different epitopes on a BSA molecule. Our ELISA system was used to detect BSA concentrations in several vaccines, such as the MMR (measles, mumps and rubella) vaccine, hepatitis A vaccine, and hepatitis B vaccine. Moreover, we compared the mAb ELISA and the present pAb ELISA by detecting BSA standards and bovine serum samples. The results showed that our ELISA system was in good accordance with the pAb ELISA system. A pair of mAbs (FMU-BSA NO.6 and FMU-BSA NO.11) from 11 murine hybridomas secreting BSA-specific mAbs was selected for the development of the sandwich ELISA. The detection limit of this quantitative assay reaches 0.38 μg/L, which is 10-fold more sensitive than those previously reported. The quantitative range of BSA concentration is from 0.5 to 40 μg/L, which is comparable to the currently used polyclonal antibody (pAb) ELISA. Intra-assay and inter-assay coefficient variations are both lower than 10% at the three concentrations used (10, 20, and 40 μg/L). Thus, the mAb sandwich ELISA developed herein may provide a stable, precise, and highly sensitive method for quantifying BSA, which is very useful in the quality control of some vaccines.