Injectable and biocompatible polysaccharide hydrogels are ideal scaffolds for drug delivery and tissue engineering. Here, we report a new in situ forming hydrogels by self-crosslinking chitosan and a biocompatible polymeric crosslinker, oxidized alginic acid. The dialdehyde alginic acid was synthesized by the oxidant reaction of alginic acid with sodium periodate. The gel was formed in situ by the Schiff base reactions between their amine groups of chitosan and aldehyde groups of alginic acid. It deformed under stress and kept its shape integrity at the strain of 40%. Sustained cargo release including rhodamine and bovine serum albumin from the hydrogels was obtained. The hydrogels were degraded by chitosanase within 30 d and the pH values of the solution remained neutral. H9c2 cells proliferated the hydrogels and maintained their native state. These results suggested this hydrogel can be promising cell therapy scaffolds for tissue engineering.