This paper is based on the result of preliminary study on the application of 4--IPOAA to culture summer seedlings of Laminaria, for the purpose of improving the technique of summer seedlings. The experiments were carried out three times in 1979-1981 . The oommon method, in reaxing the summer seedlings is usually by lowering temperatures, natural sunlight exposure and running seawater in a green house, from June to October the natural temperature of the seawater are not suitable for the growth of Lamiraria, the ove method would tape about 80---I50 days for the rearing of summer seedlings in green house. It is also rather expensive. This study was made to devise a new method in improving the technique. The main problem in the new method was to find a suitable concentration of 4-IPOAA in order to inhibit the development of the gametophytes for a certain period. The result of the experiznent are summarised in following steps: 1 .to cvllet zoospores under ordinary temperature; 2. to rear gametophytes under lower temperature for several days; 3 .to trest gametophytes with 4-IPOAA before the formation of gametes; 4 .to stop the treatment with 4-IP4AA and culture gametoytes under optimal conditions; 5. to culture seedlings about 50 days. The seedlings thus reared was found to be very healthy and grow normally. A large scale experiment will be carried out to find the posibility of using this method for cultivation industry.