Ionic- (iGG-MA) and photo-crosslinked (phGG-MA) methacrylated gellan gum hydrogels have been proposed as biomaterials for supporting nucleus pulposus (NP) regeneration and/or repair. In this study, the mechanical stability and biocompatibility of these hydrogels have been evaluated in vitro. Human intervertebral disc cells obtained from herniated patients were cultured within both hydrogels, for 1 up to 21 days. Dynamic mechanical analysis and biological characterization (Live/Dead assay, ATP and DNA quantification, PCR and immunocytochemistry) were performed after specific times of culturing. The in vitro study showed that both cell loading and culturing time do not affect the mechanical properties of hydrogels. In addition, the iGG-MA and phGG-MA hydrogels showed to be effective on supporting cells encapsulation and viability up to 21 days of culturing. In vivo biocompatibility screening was also performed, by subcutaneous implantation of both hydrogels in Lewis rats for the period of 10 and 18 days. Haematoxylin & eosin staining revealed that the hydrogels do not elicit necrosis, calcification or acute inflammatory reaction. The present study demonstrates that the iGG-MA and phGG-MA hydrogels support cells encapsulation and viability, and are well-tolerated, stable and non-cytotoxic in vitro and in vivo, thus possessing promising features for finding application as viable NP substitutes.