Aims: Compared with non-rapid eye movement (NREM) sleep, rapid eye movement (REM) sleep is characterized by low-voltage and fast electroencephalographic activity, loss of muscle tone, or intermittent muscle twitches. Waking up from REM sleep is necessary for staying alert in animals, yet it is not well known about the mechanism of the transitional signature of REM sleep. Methods: Neuronal activities of the rostromedial tegmental nucleus (RMTg), a structure in the midbrain that is primarily composed of GABAergic neurons, were manipulated using optogenetics. Electroencephalogram and electromyogram were recorded in vesicular GABA transporter (VGAT)-Cre mice. Optogenetics combined with patch clamp was employed to assess functional connectivity between RMTg GABAergic neurons and the targeted neurons. Results: Specific activation of RMTg GABAergic neurons immediately terminated REM sleep and promoted REM sleep-to-arousal transitions. In contrast, laser-mediated inactivation during NREM and REM sleep, respectively, completely converted NREM to REM sleep and prolonged the duration of REM sleep. Optogenetic activation of the RMTg to the laterodorsal tegmental area (LDT) circuit facilitated REM sleep transitions to wakefulness. However, mice with selective interference of LDT glutamatergic neurons exhibited transitions from REM to NREM sleep. In vitro electrophysiological recording showed that there are disinhibitory connections from RMTg GABAergic neurons to LDT glutamatergic neurons. Conclusions: Our findings reveal that RMTg GABAergic neurons are essential for controlling the termination of REM sleep and facilitating REM sleep to wakefulness. Acknowledgements: National Natural Science Foundation of China (32371033, 32170983, 81571296) and Shanghai Science and Technology Commission (21ZR1408000).