Display omitted •Novel Bio-PCMs with desirable biocompatibility were developed.•The composites exhibit high phase change enthalpies (156.8 J/g).•The composites show excellent thermal and shape-stabilities. Phase change thermal storage technology is an effective approach to solving the mismatch between energy supply and demand. However, this technique requires considerable efforts to the successful application and popularization. In view of designing form-stable phase change materials (PCMs) with desirable latent heat enthalpy. We reported novel and eco-friendly PCMs via a simple and convenient method. In this study, the polyethylene glycol (PEG) was in situ-loaded with Ca2+-crosslinked sodium alginate (SA) on the account of the coordination of Ca2+ with carboxyl groups in the SA structure, to produce the Bio-based composite PCMs (Bio-PCMs). The PEG/SA composites (PSCs) achieved a 93% PEG loading rate, and phase transition enthalpy can reach 156.8 J/g. Meanwhile, these materials possess satisfactory shape stability as well as excellent thermal energy management capability. Therefore, this novel composite shows considerable potential applications in the field of biomedical thermal insulation due to their biocompatibility, nontoxicity and high latent heat during phase change.