The water status in agar medium affects the regeneration of plants in the plant tissue culture that utilizes agar as a gelation substance. The followings were studied : the embryo derived from microspore of Brassica napus was chosen as experimental plant material, the matric component of the water potential of the agar medium was measured by the sand column method, and the relationship between the regeneration rate of plants and the matric potential of agar medium was analysed.With the increase of the agar concentration, both the moisture content in filter paper placed on the agar medium and the matric potential of the agar medium decreased.The embryos yield from microspore cultures of B. napus was subcultured by transplanting the embryos to : (1) the B 5-2 agar medium, and (2) the filter paper placed on the same medium. The matric potential of -2.7 kPa--5.5 kPa for the case (1), and -3.5 kPa for the case (2) made the regeneration rate of plants reach to more than 70%. The growth status and regeneration of plants were different due to the variation of the matric potential of the agar medium.