For the purpose to improve the quality of Gracilaria agar two methods of alkalitreatment were studied. (1) Cold alkali treatment method: Dried Gracilaria was treatedwith Baume 10-45° NaOH at room temprature for 5-40 days. (2) Hot alkali trea-tment method: Dried Gracilaria was treated with Baume 5-35° NaOH at 75° or 90℃.for 2-6 hours. After alkali treatment the seaweeds were washed thoroughly to removethe remaining alkali, and then the agar was extracted with water in the ordinary way.The results were summarized in the following: The gel strength of Gracilaria agar is increased markedly by both cold and hotmehtod. The Gracilaria harvested in Wanning, Hainan Island, Guangdong Province, waspretreated either by cold or by hot method, their gel strength was increased about fourtimes from below 60 g/cm~2 to about 300 g/cm~2. While the Gracilaria harvested inBeihai, Guangxi Province was subjected to pretreat by the cold method. their gelstrength was increased about ten times, from below 60 g/cm~2 to about 700 g/cm~2. The effect of treatment was related closely to the temperature, time of treatmentand the concentration of sodium hydroxide. In the cold alkali treatment method, Gracilaria was treated with Baume 30-35°alkali for only five days, its gel strength reached to maximum. In case of the concentra-tion of alkali is above Baume 35°or below Baume 30°, the time of treatment should belonger. The yield of agar by the cold method was much higher than that by the hotmethod. Therefore the cold alkali treatment method in comparision with the old hotmethod should be recognized as a better one.