Injectable hydrogels as an important biomaterial class have been widely used in regenerative medicine. A series of injectable poly(l-glutamic acid)/alginate (PLGA/ALG) hydrogels were fabricated by self-cross-linking of hydrazide-modified poly(l-glutamic acid) (PLGA-ADH) and aldehyde-modified alginate (ALG-CHO). Both the degree of PLGA modification and the oxidation degree of ALG-CHO could be adjusted by the amount of activators and sodium periodate, respectively. The effect of the solid content of the hydrogels and oxidation degree of ALG-CHO on the gelation time, equilibrium swelling, mechanical properties, microscopic morphology, and in vitro degradation of the hydrogels was examined. Encapsulation of rabbit chondrocytes within hydrogels showed viability of the entrapped cells and good biocompatibility of the injectable hydrogels. A preliminary study exhibited injectability and rapid in vivo gel formation, as well as mechanical stability, cell ingrowth, and ectopic cartilage formation. The injectable PLGA/ALG hydrogels demonstrated attractive properties for future application in a variety of pharmaceutical delivery and tissue engineering, especially in cartilage tissue engineering.