The paper reports the notable effect of the triacontanol upon theinitial growth of Laminara japonica. Before cultivated, the thalli are immersed indifferent concentrations of triacontanol solutions (0.25. 0.5, 1ppm) for six hours.Ten days later, the length of kelps, compared with the check, increases by 26%,50% and 48% respectively, and the superiority in growth can continue to a fairlylong period. Moreover, the thickness of the fronds also exceed that of the controlfrom fourty days after treatment. The results show that the positive effect on growth is closely connected withthe stimulation of the physiological activities. The triacontanol makes a notableeffect on photosynthesis in the first twenty days. The triacontanol also plays anactive role in the absorption of phosphate and nitrate, and this effect can remainfor quite a long time. Besides, the content of nucleic acids increase in the processand it implies a possible mechanism of the growth promotion by the triacontanol.