The present invention provides a polypeptide SE36 derived from the N-terminal domain (47 kd) of SERA (serine-repeat antigen) produced by malaria parasite, Plasonodium falciparum, at the erythrocyte stage, a process for purifying said polypeptide, and a malaria vaccine and diagnostic agent using as an active component said purified antigen obtained therefrom. SE36 can be produced in Escherichia coli on a large scale by deleting all or part of polymerized serines of the 47 kd serine-repeat region, whereby high purification is permitted. The human IgG3 antibodies specifically binding to SE36 prevents highly effectively growth of the protozoa in the red blood cells to inhibit fever and cerebral malaria, and further prevent the death.