Abstract: The development of female flower, megasporegensis and the development of embryo of Fraxinus mandshurica were observed by the paraffin sectioning method. The tree species was dioecious and usually bloomed in May. Female flower bloomed about a week after pollen luxuriantly released. The stigma was receptive as soon as female flower opened. Female flower had two rudimental stamens beside its ovary. The ovary was twicarpellum, twilocular with two anatropous ovules each loculus. The ovule was unitegmic and tenuinucellar. The archesporium was unicelled. The development of embryo sac was of the Polygonum type. Four megaspores arranged linearly. Generally the megaspore of the chalaza was functional, while a few functional megaspores came from the second megaspore at the chalaza site or the two at the micropylar and chalaza sites. Endosperm was nuclear type. The embryogeny conformed to Asterad type, which passed through proembryo, heart, torpedo and cotyledonary stages. The embryo finished morphological differentiation in the end of June. Only one of the four young ovules developed to mature seed and every seed had one embryo in general. The typical embryological characteristics and some abnormal phenomena in embryogenesis of F. mandshurica were discussed.

Key words: Fraxinus mandshurica, Female flower, Megasporogenesis, Embryo development