Abstract In this report, biological macromolecular full IPN hydrogel fibers composed of gelatin and alginate with an interpenetrating network (IPN) structure were prepared by wet spinning using a combination of enzymatic and calcium ions crosslinking. In the full IPN hydrogel fibers, mTG catalyzed the formation of one network of gelatin while calcium ions crosslinked another network of alginate intertwining with the former. The mechanical strength of the full IPN hydrogel fibers was measured by an electronic single fiber strength tester. The results showed that gelatin–alginate full IPN hydrogel fibers had a significant improvement of mechanical strength over gelatin–alginate semi-IPN gel fibers crosslinked only by calcium ions. The full IPN fiber has the highest tension of 62cN and elongation of 739%, which are much higher than those of alginate hydrogel. Furthermore, biological evaluation indicated that gelatin–alginate full IPN hydrogel fibers enhance cell adhesion and proliferation significantly, illustrating the cyto-compatibility. A preliminary trial of hand weaving showed the knittablity of the mechanically tough full IPN hydrogel fibers. Because of their both excellent biocompatibility and mechanical strength, the biological macromolecular hydrogel fibers with full IPN structure may be desirable candidates for engineering tissue scaffolds.