A hemostatic sponge prototype was successfully synthesized from fish gelatin as an alternative to mammalian gelatin, which was mixed with alginate in certain combinations and double cross-linking of calcium ions and gamma irradiation at a dose of 20 kGy to improve the characteristics and effectiveness of its function as a local hemostatic agent. There was an improvement in the physicochemical and mechanical properties, porosity index, absorption capacity, biodegradation properties, biocompatibility, and hemocompatibility of the FGAS prototypes compared with the pure fish gelatin sponge. Hemostatic activity tests showed that the means of clotting time, prothrombin time, and activated partial thromboplastin time were shorter in the FGAS prototype than in the negative control, and there was no significant difference compared with the commercial gelatin sponge. The hemostatic mechanism of the FGAS prototype combined a passive mechanism as a concentrator factor and an active mechanism through the release of calcium ions as a coagulation factor in the coagulation cascade process.