Abstract: The spores of two selected strains and a common cultivated strain of Laminaria japonica were used to study the effects of vitamin C on the growth and maturation rates of female gametophytes. The spores were collected on slides. The treatment of vitamin C was given to young gametophytes at 7–10 ℃. Three concentrations were used, 100 ml of sea water contained 1 mg, 10 mg and 100 mg of vitamin C respectively. The main results of the study are summarized as follows: (1) While the female gametophytes were mainly unicellular at low temperature, they tended to grow larger and become many-celled with the addition of vitamin C, the higher the concentration and the longer the treatment of vitamin C, the more prominent being the effects. (2) The maturation of female gametophytes were delayed by vitamin C as much as one month after three times of treatment. (3) There were significant differences in the growth and maturation rates of female gamtophytes treated with vitamin C in the same strain and between the two strains used in the experiment. As definite and indefinite variations were observed under the same condition, it was thus assumed that there were genetic differences among the female gamtophytes. The induction of mitosis by vitamin C in female gametophytes might be of some practical significance for cytological studies and breeding work through hybridization.