A dual pH- and temperature-responsive physically crosslinked and injectable hydrogel system was developed for efficient and long-term delivery of oncolytic adenoviruses (Ads). Three different types of physically crosslinked hydrogels with different chemical compositions and properties were prepared. These hydrogels with good biocompatibility can be injected at pH 9.0 and room temperature and rapidly form a gel under body or tumor microenvironment conditions. Ads encapsulated in hydrogels were released gradually without burst release. Moreover, these physically crosslinked hydrogels provided a protective environment for Ads and maintained their bioactivity for a long period of time. Compared to naked Ads, Ads protected by these physically crosslinked hydrogels showed strong cytotoxicity to cancer cells even after 11 days. The Ad-loaded hydrogel system also exhibited enhanced and long-term antitumor therapeutic effects in human xenograft tumor models. Due to these outstanding properties, Ad-loaded injectable hydrogels might have potential for long-term cancer treatment.