The accumulation of proteins in the jackfruit seeds was monitored by extracting seeds proteins at various stages of growth. The early developing seed had several protein bands distributed over a molecular weight range of 10-67 kDa. But the mature seeds contained fewer bands with two of them being prominent at 12 and 15.4 kDa. Upon isoelectric focusing, the mature seed proteins were resolved into several bands distributed over a pH range of 4-9. While the mature seed proteins contained powerful hemagglutinating activities, these were not detected in the early developing seed. In contrast, the early developing seed had immunoglobulin A (IgA) binding activity as determined by enzyme-linked immunosorbent assay (ELISA). By Western blotting it was found that the early developing seed contained a novel 10 kDa IgA binding protein that was not present in the mature seeds.