The medial prefrontal cortex (mPFC) plays a crucial role in the control of social behaviour. However, its projections to the medial preoptic area (MPOA) have not been investigated. Our research team has previously shown that ascending inputs to the MPOA increase the extent of social interactions between rats. Therefore, we determined the projection pattern of mPFC neurons projecting to the MPOA and examined their role in social behaviour. Retrogradely transferred adeno-associated virus (AAV) expressing Cre recombinase was injected into the MPOA followed by an mPFC injection of an AAV encoding stimulatory and inhibitory designer receptors coupled with mCherry fluorescent protein. Retrogradely labelled neuronal cell bodies were found in the infralimbic and prelimbic cortex. mCherry-labelled fiber terminals were detected in several subcortical areas, such as the accumbens nucleus, ventral pallidum, lateral septum, paraventricular and ventromedial hypothalamic nuclei, and medial amygdala suggesting that mPFC neurons projecting to the MPOA give rise to collaterals to these brain regions. In addition, we used vGAT-ZsGreen transgenic animals to investigate if subcortically projecting mPFC neurons are GABAergic. When stimulating the mPFC neurons projecting to the MPOA, reduced sociability was found in the three-chamber test while inhibition did not change the social behaviour. When inhibiting the mPFC neurons projecting to the MPOA, the duration of anogenital sniffing and mounting were increased. In conclusion, the chemogenetic manipulation of the examined mPFC projection neurons exerted an effect on the sociability of the animals indicating their role in regulating social behaviours. Grant support: NAP3 (NAP2022-I-3/2022), NKFIH OTKA K134221, K146077