Abstract: Some organelles of watermelon microspores were observed by using transmission electron microscope.Ribosome density was high in tetrad microspores, very low in vacuoli zing ones, and high again after vacuolization came to an end.Mitochondria showed a cycle of dedifferentiation and redifferentiation.Disappearance of mitochondrial cristae and decrease of such organelle number during vacuolization stage were implications of the dedifferentiation, and reappearance of cristae and a variety of variations in shape after vacuolization indicated the redifferentiation.Plastids showed no structural modifications, but underwent evident changes in size.Most individuals reduced by several times when microspores were in va cuolization process, and then enlarged several times again after the process.Endoplasmic reticula changed from smooth type in tetrad microspores to rough type in vacuolized ones.Dictyosomes were copious before vacuolization, sparse after vacuolization stopped.It is evident that cytoplasm of watermelon microspores was reorganized.Cytoplasmic reorganization might be an inherent characteristic, for it conformed to spore development and was necessary for further development into 2 celled pollens.