Carrageenans are highly sulphated galactans, well-known for their thermogelation properties which have been extensively exploited in food and cosmetics industry but poorly explored in the biomedicine field. In this study we have assessed the in vitro and in vivobiocompatibility of κ-carrageenan hydrogels that have been explored for regenerative medicine and tissue engineering applications. The in vitro cytotoxicity of the materials using a L929 mouse fibroblast cell line was evaluated, and next the effect of κ-carrageenan hydrogels on the activation of human polymorphonuclear neutrophils cells (hPMNs) by the quantification of reactive oxygen species (ROS) by chemiluminescence. Subsequently it was studied the inflammatory/immune reaction to κ-carrageenan hydrogels upon subcutaneous implantation in rats. Explants were retrieved after 1 and 2 weeks of implantation, for histological and RT-PCR analysis. The cytotoxicity screening revealed that κ-carrageenan hydrogels did not significantly affect L929 metabolic activity. Moreover, hPMNs contact with κ-carrageenan resulted in a reduced and a neglectable signal regarding the detection of superoxide and hydroxyl anions, respectively. The results from the in vivo experiments indicated that κ-carrageenan induce a low inflammatory response. Overall, the data obtained suggests that κ-carrageenan hydrogels are biocompatible and thus can be further studied for their use in target biomedical applications.