Cellulase enzymes have been widely used in many industrial activities, such as the production of biofuels, biofertilizers, and bio-decomposers. The usage of cellulase enzymes on an industrial scale usually involves a relatively high temperature. Microorganisms in marine ecosystems are widely known to have the ability to produce cellulase enzymes in various environmental ranges. However, exploring marine cellulolytic bacteria at low temperatures still lacks information. This study aims to determine the cellulolytic activity of bacteria associated with seagrass ecosystems at low temperatures. Cellulolytic activity test used selected bacteria isolates from the seagrass ecosystem (actinobacteria: AA10b, AA11a, AA30a, AB22b; heterotrophic bacterial: HB1.1, HB2.1, HT1.2, HT2.2). The cellulolytic index values were obtained from the clear zone test on CMC 1% medium with congo red staining (actinobacteria) and iodine (heterotrophic bacteria) in different temperature treatments (4°C, 17°C, 20°C, and 40°C). The results showed that all isolates had various cellulolytic index values at different temperatures. There was no bacterial cellulolytic activity at 4°C. However some isolates showed activities at 17°C and increased as the temperature was higher. The highest production of cellulolytic activity occurred at 40°C for both actinobacteria and heterotrophic bacteria isolates. The actinobacteria isolate AA11a had the highest cellulolytic index of 7.00 at 40°C. This study indicates that at low temperatures, associative bacteria from the seagrass ecosystem have considerable cellulolytic activity for further research applications in various industries.