We have established that the posterior intralaminar thalamic nucleus (PIL) receives ascending input from the somatosensory system and promotes social grooming in female rats. In the present study, we focused on the role of PIL neurons in aggressive behavior. For chemogenetic manipulation of PIL neurons, we injected AAV into the PIL, which expressed excitatory and inhibitory DREADD. In a separate experiment, we selectively tagged socially c-Fos-activated neurons in the PIL. On the first day of the experiments, a vehicle was injected followed by male intruder test 1.5 hours later. On the next day, the same test was repeated with clozapine-N-oxide (CNO) administration to activate the DREADDs. Chemogenetic stimulation decreased aggression and increased positive valance contacts while inhibition of the PIL neurons had the opposite effect. To establish activation we measured the number of c-Fos-ir neurons. The inhibition of PIL neurons during aggressive behavior decreased c-Fos expression in the PIL and in the medial preopic area (MPOA), while CNO injection into animals with stimulatory DREADD activated the PIL and the MPOA in the absence of social interactions. We also investigated the PIL-MPOA pathway by injecting AAV into the PIL and local CNO injection into the MPOA via intracerebral cannulas to activate and inhibit the fiber terminals in the MPOA. The activation of the pathway decreased aggression and increased positive valance contacts. Based on these results we suggest that PIL neurons reduce aggressive behavior possibly by their projections to the MPOAGrant support:ÚNKP-23-3-II-SE-48,EFPO-3.6.3-VEKOP-16-2017-00009,MTA National Brain Program 3.0,NKFIH OTKA K134221.