1. It is recommended to extract the Gracilaria agar by steam in an autoclaveor an open kettle to shorten the extracting time and to facilitate the filtration. Ex-traction of Gracilaria agar under 3 lb/in² of steam pressure with 30-or 40-fold ofwater for 1 to 1(1/2) hour and then with 15-fold of water for a half hour, seemedto be more preferable (Table 1, 2,3). 2. When NaOH or KOH was used as an extracting reagent, the gel strength ofagar obtained was highly increased, and NaOH appeared to be more effective thanKOH(Table 4). The mixed reagents of NaOH and KH₂PO₄showed more marked effecton the yield of agar than did NaOH alone. But the effect of the combination of NaOHand neutral salts solution was about the same as the NaOH alone (Table 5), andvarious salts without NaOH exhibited no distinct effects (Table 6). 3. On the addition of K, Ca, Mg salts to the agar sol, their gel strength wasenbanced in spite of whether or not being heated (Table 7), while the agar sol, trea-ted with NaOH + KH₂PO₄ under 5 lL/in² of steam pressure for 1 - 2 hours, and thencooled, thawed and dried, also gave a higher gel strength with about 60% of re-covery (Table 8). 4. The extracted liquor from Gracilaria after adding alkali and heating gave ahigker gel strength than untreated, while no distinct change was observed if inorga-nic salts were added (Table 9). Our experiment on the effect of different heatingtime upon the extracted liquor treated with alkali indicated that their gel strengthincreased with the increase of heating time under 3 lb/in² of steam pressure, but theyield was relatively low. Judging from the gel strength, the treatment with 1% NaOHunder 3 lb/ in² of steam pressure for 2 hours seemed to be an optimum condition inobtaining a good quality of agar (Table 10). 5. The Oretreatment of Gracilaria with NaOH + CaCl₂ or NaOH alonet showedno marked difference in the gel strength of agar. In the alkali-treated liquor rem-ained about 10 % of agar, whick might be recovered by freezing-drying. The thalliof Gracilaria after treatment with alkali ought to be washed as thoroughly as possiblewith runniug water before the extraction to remove the alkali, or neutralized withacid, and were then subjected to extraction (Table 11).