Abstract: Optical microscopy，confocal microscopy and scanning electron microscopy were used to observe the micromorphological characteristics of basidia and basidiospores at different stages of development in Agaricus bisporus. The basidia grows closely together and the proportion of different types of basidia in the gill at different developmental stages is not sustained. In the early stage of development，wich is the top of the basidium was covered with membrane（Apical Membrance of Basidium，AMB）. In basidium development，the two nuclei fused in the middle of the basidium，and the nuclear phase of the basidium changed during its development. The formation of mononuclear cells migrated back to the top of the basidium and meiosis took place. Finally，four nuclei were formed at the top of the basidium. Sometimes，the second meiosis was different and the phenomenon of three nuclei appeared in the head of the basidia due to the non-synchrony of the secondary mitosis. After meiosis，an average of four nuclei migrated to the sporozoites. Basidiospores wall have two layers. The basidiospores contain lipid droplets of uneven sizes.

Key words: Agaricus bisporus, morphological observation, nuclear phase change