Aims. Though electrophysiological methods allow recording neuronal activity from freely moving animals, the localization and type of cells recorded can only be deduced from indirect markers. Two-photon microscopy can provide exact localization and immediate identification of cell types. Our aim was to develop and test an imaging modality that is capable of deep-tissue long-term two-photon imaging while being light and compact for a mouse to carry while freely moving in its environment.Methods. All experimental procedures were approved by the French ethics committee (APAFiS #30959) and were conducted in agreement with the European Council Directive 86/609/EEC. Adult wild type Swiss mice were used, expressing GCaMp8m in the hippocampus (viral injection at P0; pGP-AAV-syn-jGCaMP8m-WPRE), based on a previous approach for building a hippocampal window (Villette, 2015 Neuron). We have developed an endoscope system (InSplorer, Lightcore Technologies) that is based on a hollow-core fiber (Septier, 2022 OpticsExpress) and allows scanning speeds up to 20Hz and a field-of-view of up to 500µm. Before the imaging sessions, the endoscope was attached to the mouse head using a custom-made head helmet and baseplate.Results. The endoscope system was tested for both head-fixed and freely moving conditions. We show that the animals were not impeded by the endoscope, since they followed standard movement and behavior patterns such as grooming, jumping, rearing and running. The repeated hippocampal imaging sessions prove that longitudinal studies are possible.Conclusions. We conclude that the InSplorer endoscope system is a feasible approach for long-term deep two-photon imaging in freely moving mice.