The progress in brain diseases treatment is limited by the blood-brain barrier (BBB), whichprevents delivery of the vast majority of drugs from the blood into the brain. In this study, wediscover unknown phenomenon of opening of the BBBB (BBBO) by low-level laser treatment (LLLT,1268 nm) in the mouse cortex. LLLT-BBBO is accompanied by activation of the brain drainagesystem contributing effective delivery of liposomes into glioblastoma (GBM). The LLLT inducesthe generation of singlet oxygen without photosensitizers (PSs) in the blood endothelial cells andastrocytes, which can be a trigger mechanism of BBBO. LLLT-BBBO causes activation of the ABCtransportsystem with a temporal decrease in the expression of tight junction proteins. The BBBrecovery is accompanied by activation of neuronal metabolic activity and stabilization of the BBBpermeability. LLLT-BBBO can be used as a new opportunity of interstitial PS-free photodynamictherapy (PDT) for modulation of brain tumor immunity and improvement of immuno-therapy forGBM in infants in whom PDT with PSs, radio- and chemotherapy are strongly limited, as well as inadults with a high allergic reaction to PSs.