Abstract: Haploid rice plantlets were induced from cultured ovaries in our previously reported experiment. The present paper is an embryological study on this subject. Young flowers of two japonica cultivars were excised and cultured just in the same manner as before. Liquid medium used for float culture was N6+3% sucrose+0.125 ppm MCPA. The inoculated materials were checked to be at late uninuclcate pollen stage which corresponded mainly to the uuinuelcate embryo sac stage, but as well as some 2- or 4-nucleate embryo sacs. Samples were fixed at 23 days intervals in acetomethanol (1:3), stained in toto with diluted Ehrlich's hematoxylin and sectioned by paraffin method for microscopical observation. 4 days after inoculation most of the embryo sacs developed up to 8-nucleate stage with polarized differentiation of the egg apparatus, central cell and antipodals. From 7th day on, proembryos of various sizes and shapes appeared in the micropylar region of some embryo sacs; some consisted of meristcmatic ceils, others were highly vacuo]ated. One-celled as well as linear multicellular suspensors atypical of in vivo zygote proembryos were observed, ttowever, it was uncertain whether the proembryos originated from the egg cell, the synergids, or the differentiating egg apparatus as a whole. Another peculiar event occured during culture was the formation of endosperm-like free nuclei from the unfertilized polar nuclei in some embryo sacs. Sometimes the free nuclei were numerous and showed a tendency of cell formation in localized areas. 12–15 days after inoculation, the proembryos developed into mieroseopieal ealli with globular or pearlike shape, wbieh continued enlarging to visible size with naked eyes at about 18–24 th day. Further growth eventually led the ealli protruding out the ovary wall beyond 32–35 the day. These observations indicate that the embryo sue, similarly as the pollen, can be induced to embryogenesis in vitro. This may open a new way to study the mechanism controlling gametophytie and sporophytie developmental pathways of embryo sac and provide means for large-scale production of "embryo sac plants" in future.