Carrageenan oligosaccharides have attracted significant attention due to their excellent biological activities, and they can be produced by carrageenases. In this study, a novel marine bacterium, Shewanella sp. LE8, was used to enzymatically degrade carrageenan, and the κ-, ι-, and λ-carrageenases produced by the bacterium were characterized. The crude enzyme derived from media exhibited κ-carrageenase activity, indicating its natural secretion during growth and proliferation. According to the results of molecular weight distribution from HPGPC, λ-carrageenan could be degraded by Shewanella sp. LE8 cells in both 20 mM Tris-HCl buffer and PBS, while ι-carrageenan can only be hydrolyzed in PBS environment, indicating the activation of ι-carrageenase in Shewanella sp. LE8 was dependent on the presence of Na