Substrates for seaweed culture with recycled glass powder and foaming agent were prepared. To simulate manufacturing conditions, 5% addition of foaming agent and a sintering temperature of 790°C were most suitable. The substrates on which saprophytes (seedling) of brown alga Ecklonia kurome were attached were submerged in seawater at St 1 in the Yatsushiro Sea. However, cultivation was not successful because of the predation of some fish. The thin rope (1.2m long) on which the saprophytes of brown alga Laminaria japonica were attached were surrounded on the substrate (14cm×16cm), and was cultured in the sea (St. 2) beginning 26 December, 2005. The growth was monitored monthly, and the final growth at 199 cm in maximum blade length, 11.9cm in maximum blade width and 112g in maximum individual wet weight were obtained on 12 May, 2006. The number of fronds per substrate was 66, and the final yield during this period was 3.7kg. From the results, an attempt to utilize recycled glass as a substrate for seaweed cultures was considered to be successful.