Seaweed plays a significant role in reducing green-house gasses (GHG) emitted by ruminant animals, in particular methane gas (CH4) generated during rumen fermentation of the feed. Euchaema cottonii is one of potential cultivated seaweed in tropical country. A preservation procedure is necessary for further application in CH4 reduction program. The study looked at how three drying methods (sun drying, oven drying, and freeze drying) affected the E.cottonii ability in reducing CH4 methane as measured by an in vitro technique. The addition of dried E. cottonii up to 4% dry matter (DM) was tested using rice straw diets mixed with concentrate in the ratio of 70%:30% in DM base. Measurements was conducted on gas production, degradability and end product of rumen fermentation during 48-hour incubation using a gas production system and ANKOM Daisy II techniques. Overall, the three dried products of E. cottonii found to considerably lower production of CH4, increased DM and OM degradability as well as total VFA production (P<0.05). The three treatments have no effect on NH3 concentration and the bacterial population, but decreased protozoa population (P<0.01). The lowering of CH4 gas production in the rumen is impacted by all three drying methods in the same way. It is concluded that dried E.cottonii addition up to 4% DM effective in depressing enteric CH4 production, without causing negative effect on DM and OM degradability as well as did not depress total VFA formation and bacterial activities. The three different drying-methods have similar effect on reducing CH4 production, with the most affective is freeze-drying method.