The lateral hypothalamus (LH) is a central node of the brain to mediate brain states. It is comprised of highly heterogeneous neuronal populations and diverse projections. It remains elusive how different neuronal LH subdivisions mediate the brain state. Here, we developed an optogenetic method to map LH functional projections and investigate functional connectivity upon LH activation. Optical stimulation of the LH can directly activate the preoptic area, central thalamus and the subiculum area, and increase the cortical resting-state correlation. This work makes it possible to further target different LH neuronal populations and decipher cell-type specific functional projections.