Abstract: Diplomonads seem to be the most primitive archezoa.In literature,almost all the studies on diplomonad nuclear division were accomplished under light microscope,Considerring the primitiveness of diplomonad nucleus,we investigated the nuclear division of cultivated Giardia lamblia with routine electron-microscopy preliminarily.Nuclear envelope was found to be preseved during the whole division process.Spindle or spindle microtubules were never found within dividing nucleus or cytoplasm.No condensed metaphase chromosomes were observed,although heterochromatin could occationally be seen both in dividing nucleus and in interphase nucleus.If there is surely no spinde participating the division process,then colchcine should have no influence on this process.Our experiments showed that various concentrations of colchicine (0.1-20 μg/ml),certainly had no effect on the cell division of Giardia.Immuno-fluorescent microscopical detection was done with anti-tubulin antibody and it was found that no tubulin or tubulin-made structure existed in the interphase nucleus and dividing nucleus,while cytoplasm and flagella gave strong positive reaction.The resuts described above suggested that there is no spindle formed during the nuclear division of Giardia.The possible significance of this phenomenon in the origin and evolution of mitosis was discussed.