Appropriate preference for light or dark is crucial for animals survival,but the underlying circuit mechanism is largely unknown.Here,by combining behavioral assay,in vivo optoand electro-physiological recording,optogenetic manipulation and morphological tracing in zebrafish larvae,we demonstrated that a circuitry consisted of retinal ganglion cells(RGCs),thalamus and left dorsal habenula(ldHb)mediates the light-dark preference.