In situ forming hydrogels are widely explored as injectable drug delivery systems for biomedical applications. It is important for these hydrogels to undergo gelation and deliver the drug in a timely manner upon administration. In this study, lysine-rich elastin-like polypeptide (ELP) and aldehyde-presenting alginate are crosslinked via Schiff base formation under ambient conditions to generate hydrogel. The physicomechanical and drug release properties of the alginate-ELP hydrogel are conveniently controlled by the concentrations of alginate and ELP. Furthermore, due to the thermoresponsiveness of ELP, the alginate-ELP hydrogel undergoes reversible swelling/deswelling at the transition temperature near the physiological temperature. Therefore, the drug release from the alginate-ELP hydrogel is expedited via thermoresponsive deswelling. Taken together, the in situ forming alginate-ELP hydrogel is a highly attractive injectable drug delivery system capable of programmable release characteristics.