A variety of polymer- and ceramic-based soft-tissue adhesives have been developed as alternatives to surgical sutures, yet several disadvantages regarding the mechanical properties, biocompatibility, and handling hinder their further application particularly when applied for immobilization of implantable devices. Here, it is reported that a biocompatible and tough metal, titanium (Ti), shows instant and remarkable adhesion properties after acid treatment, demonstrated by ex vivo shear adhesion tests with mouse dermal tissues. Importantly, in vivo experiments demonstrate that the acid-treated Ti can easily and stably immobilize a device implanted in the mouse subcutaneous tissue. Collectively, the acid-treated Ti is shown as a solid-state instant adhesive material for biological soft tissues, which can have diverse applications including immobilization of body-implantable devices.