This experiment was conducted to improve inedible seaweeds as feedstuff for herbivores using seaweeds (Sargassum associations) produced in Cheju together with corn silage and sweet potatoes. In Experiment Ⅰ, pH changes of the ground seaweed dissolved in acid and alkaline solutions were measured at various times of soaking. In Experiment Ⅱ, whole seaweed and corn silage were mixed for further fermentation, and seaweed and sweet potatoes were proportionately mixed for silage. Chemical analysis of organic acids and evaluation of silage qualities were done by the method proposed by Flieg. These experiments have been carried out from April 1st, 1975 to March 25th, 1976. The results summarized are as follows: Experiment Ⅰ. To measure pH values of the ground seaweeds in the acid and alkaline solutions as a results of ion exchange and other effects, hydrochloric acid, sulfuric acid and sedium hydroxide solution of 0.1N, 0.05N and 0.01N were added separately to each of the ground seaweed plots for pH tests at various intervals of time. The results of experiment I are as follows: 1. Both of hydrochloric acid and sulfuric acid plots show generally similar changing pattern of pH values. Within 30 minutes of time pH values of both acid solutions were enhanced from pH 1.0(0.1N), pH 1.6(0.05N), and pH 2.0(0.01N) up to pH 3.6, pH 4.2 and pH 4.4 respectively after mixing with ground seaweed. 2. In sodium hydroxide solutions of pH 13.2(0.1N), pH 13.0(0.05N) and pH 12.6(0.01N), pH values of the ground seaweed fell down to pH 6.4, pH 7. 2 and pH 5.8 respectively showing near to neutralization within 30 minutes of soaking time. Experiment Ⅱ. To estimate the effects of seaweeds on corn silage, seaweeds were added to corn silage to store for fermentation at room temperature for six months. To make A.I.V. silages of seaweeds mixed with sweet potatoes, 11 combinations of mixtures were filled into each plastic bottles and fermented for 25 days in water bath maintained at 25℃. The results obtained are as follows: 1. Seaweeds added to corn silage caused decreased organic acid production and slightly higher pH value than that of control plot. No difference was found in lactic acid production in both treatments of silages. Highly significant difference (p$lt;0.01) was found in acetic acid production between two silages. Butyric acid production teas 0.6 mM far seaweed-corn silage and 13.9 mM for corn silage showing highly significant effects (p$lt;0.01). 2. Silages of excellent quality were produced from 11 treatments combinated with seaweed and sweet potatoes. In treatment 5 and treatment 4, some adequate proportions of combinations of samples have been brought about better results(p$lt;0.01) than single treatments in lactic acid productions. No butyric acid was found in all of the treatment plots. No difference was found in quality of silages between seaweed silage and sweet potato silage.