Some preliminary study on the Horseradish peroxidase labelled staphylococcal protein A (HRP-SpA) and its application in ELISA is described. By using HRP-SpA in ELISA for the detection of antibodies to Anthracic toxin, Japanese B encephalitis virus, thyroglobulin and Cysticercus in rabbit, human and pig sera instead of the conventional enzyme-linked second antibody such as goat anti-rabbit IgG, horse anti-human IgG and rabbit anti-pig IgG conjugates, relatively satisfactory results have been obtained. Meanwhile, the affinity of HRP-SpA to IgG from human and different mammalian species has been observed. Experiments have showed that HRP-SpA is a more stable and widely applicable immunological reagent, therefore, it is especially suitable for ELISA. No doubt, its study and application will facilitate the spread and development of ELISA technique.