Abstract: According to the investigations of the nucleus of Giardia in our laboratory and the electron-microscopical photographs of diplomonads and reports in literature,I found that diplomonad nuclei had no nucleolus and that the nuclear envelope was incomplete with large nuclear envelope openings.The ways of their nuclear division ware also all primitive.These primitive characteristics of the nucleus distinguish diplomonads from all other presentknown archezoa.Therefore,I would suggest to divide kingdom Archezoa (Cavalier-Smith,1989) into two kingdoms,Proarchezoa (including diplomonads) and Metarchezoa.Both belong to superkingdom Archezoa (Cavalier-Smith,1989).