Abstract: We used transmission electron microcopy to examine the process and ultrastructure of double fertilization in Oryza sativa. Such fertilization exhibits a unique fusing between the female and male nucleus. Direct fusion occurs only between the nuclear membranes of the female and male nucleus, instead of via mediating organelles, regardless of the presence of karyogamy between the sperm nucleus and egg cell nucleus or between the sperm nucleus and polar nucleus (secondary nucleus). Furthermore, the sperm nucleus attaches to the persistent synergid 3.5 h after pollination.