A prefrontal-thalamic circuit encodes social information for social recognition. This study identifies a critical role of the ventral midline thalamic nucleus reuniens (Re) in social recognition in male mice. The Re has reciprocal connections with the medial prefrontal cortex (mPFC) and is essential for social recognition. In vivo single-unit recordings and decoding analysis show that both mPFC and Re represent different social stimuli, but mPFC coding capacity is stronger. Chemogenetic inhibition of Re impairs mPFC-Re neural synchronization and mPFC social coding. Optogenetic manipulations reveal that reciprocal connectivity between mPFC and Re is necessary for social recognition. These results demonstrate that the mPFC-Re pathway is critical for social coding and recognition. Social recognition involves encoding social information and distinguishing unfamiliar from familiar individuals. The mPFC is known to play a role in social behavior, but how identity information is processed and communicated remains unclear. The Re, which has dense connections with the mPFC, is thought to facilitate communications in the prefrontal-thalamo-hippocampal route. Encoding of social information requires processing of multiple complex multisensory and internal cues. The mPFC and Re show distinct response patterns to different social stimuli, with mPFC neurons showing stronger responses. Population-level analysis shows that mPFC and Re neurons have prominent responses to social stimuli. Neural synchronization between mPFC and Re is important for efficient communication during social recognition. Chemogenetic inhibition of Re reduces mPFC-Re coherence, indicating that normal Re functioning is necessary for neural synchronization. Optogenetic inhibition of Re impairs social recognition, showing that Re is necessary for social recognition. Inhibition of Re also affects the mPFC's ability to encode social stimuli, as shown by information-theoretic and population decoding analyses. These results highlight the importance of the mPFC-Re circuit in social information processing and social recognition. The study provides insights into neural information processing and transmission along cortical-thalamic pathways.A prefrontal-thalamic circuit encodes social information for social recognition. This study identifies a critical role of the ventral midline thalamic nucleus reuniens (Re) in social recognition in male mice. The Re has reciprocal connections with the medial prefrontal cortex (mPFC) and is essential for social recognition. In vivo single-unit recordings and decoding analysis show that both mPFC and Re represent different social stimuli, but mPFC coding capacity is stronger. Chemogenetic inhibition of Re impairs mPFC-Re neural synchronization and mPFC social coding. Optogenetic manipulations reveal that reciprocal connectivity between mPFC and Re is necessary for social recognition. These results demonstrate that the mPFC-Re pathway is critical for social coding and recognition. Social recognition involves encoding social information and distinguishing unfamiliar from familiar individuals. The mPFC is known to play a role in social behavior, but how identity information is processed and communicated remains unclear. The Re, which has dense connections with the mPFC, is thought to facilitate communications in the prefrontal-thalamo-hippocampal route. Encoding of social information requires processing of multiple complex multisensory and internal cues. The mPFC and Re show distinct response patterns to different social stimuli, with mPFC neurons showing stronger responses. Population-level analysis shows that mPFC and Re neurons have prominent responses to social stimuli. Neural synchronization between mPFC and Re is important for efficient communication during social recognition. Chemogenetic inhibition of Re reduces mPFC-Re coherence, indicating that normal Re functioning is necessary for neural synchronization. Optogenetic inhibition of Re impairs social recognition, showing that Re is necessary for social recognition. Inhibition of Re also affects the mPFC's ability to encode social stimuli, as shown by information-theoretic and population decoding analyses. These results highlight the importance of the mPFC-Re circuit in social information processing and social recognition. The study provides insights into neural information processing and transmission along cortical-thalamic pathways.