An in vitro propagation system was developed for mass-production of hybrid rice by the multiplication of shoot primordial subjected to tissue culture (hereafter referred to as “ tissue-cultured” shoot primordial). Shoot primordial were generated and maintained from mature embryos of hybrid rice (Oryza sativa L.). N6 modified medium (hormone: 10^-6M 2,4-dichlorophenoxyacetic acid (2,4-D) and 10^-5 M cytokinin) was used. Shoot primordia maintained a high level of regeneration ability for more than one year. White bodies were formed synchronously from shoot primordia by keeping them in stationary culture at high temperature (30ー35℃) in the dark. When shoot primordia and white bodies encapsulated in calcium alginate gel containing N6 modified media without hormones were sowed in soil, they germinated but did not grow. However they germinated and grew on a sterilized medium and ripened when transplanted to pots. Compared with plants grown from seeds, the majority of the plants derived from shoot primordia, which headed earlier, showed a shorter plant height, lighter grain weight and 1000 grain weight, and the percentage of fertility of some individuals was lower.