The purpose of this experiment is to study the effect of the alkali treat-ment on the yield and properties of agar extracted from Chinese Gracilaria and toselect the suitable species of Gracilaria as raw materials for the production of agar.Specimens of Gracilaria were treated with 32% NaOH at room temperature for 5 days.Using this cold concentrated alkali method, 10 species of Gracilaria which were collectedin China were studied. The agar yield, properties and chemical composition before andafter alkali treatment are shown in table 1, and the infrared spectra are shown in figs1,2 and 3. The main results obtained are summarized as follows: 1) Agars extracted with sodium hexametaphsphate afterr alkali treatment were muchbetter than those extracted with water. The agar yield from G. asitica was 27.6-31.3%, G. tenuistipitata was 14.0-39.5%, G. sjoestedtii 22.4-27.8%, G. haina-nensis 8.6%, G. articulata 19.1% G. chorda 15.4% G, textorii 21.6%, G.euche-umoides 31.7%, G. blodgettii 27.6% and G. sp.42.6%, respectively. 2) The Gel strength of agar extracted with (NaPO₃)₂ after alkali treatment were:G. asiatica 234-1025g/cm², G. tenuistipitata 329-1035g/cm², G. sjoestedtii 375-855 g/cm², G. hainanensis 130 g/cm~2, G. articulata 87g/cm~2, G. chorda 376g/cm~2,G. textorii 10g/cm², G. eucheumoides 38 g/cm², G. blodgettii 323 g/cm~2 and G. sp.923 g/cm~2. 3) According to the results of agar yield and gel strength, G. asiatica, G. tenuistipitata and G. sjoestedtii are considered to be the better raw materials for agarproduction to other species of Gracilaria ever studied. 4) The gelation and melting temperature of agar after being treated by alkaliwere increased while the viscosity decreased. 5) The 3,6-AG content of agar isolated. from alkali-treated Gracilaria was higherthan those without alkali treatment, and the reverse relation was observed about thesulfate and galactose content. The increase of gel strength lay in the extent of thesulfate decreased and the 3,6-AG increased. 6) The effect of the alkali treatment on the gel strength of Gracilaria agarvaried with the species of Gracilaria as well as the season and location they were collected. 7) The time of gel strength increased by the cold concentrated alkali method was34.4 on the average, thus cold concentrated for method appears to be more effective.than any other alkali treatment method reported.