SummaryWe present a protocol for inducing a hibernation-like state in free-moving mice using optogenetics. We have recently developed an optogenetic technique utilizing modifiedOpsin4, which is activated by weak blue light, resulting in prolonged neuronal excitation. We describe a protocol that includes detailed instructions for virus injection, implantation of optic fibers and temperature transmitters, photostimulation, and real-time recording of body temperature in mice. This method is valuable for investigating the mechanisms underlying torpor and thermoregulation in mice.For complete details on the use and execution of this protocol, please refer to Takahashi et al.1