Objective To determine the expression of type Ⅲ interferon ( IFNL) and IFNL receptor 1 (IFNLR1) in the genital tract in rhesus macaques to elucidate the biological characteristics of rhesus macaque IFNL system and promote the use of these monkeys in studies on the pathology, drugs and vaccines for human diseases. Methods IFNL1, IFNL3, and IFNLR1 mRNA levels in normal and simian-human immunodeficiency virus (SHIV) / simian immunodeficiency virus ( SIV)-infected genital tract tissues of rhesus macaques were detected by gene-specific reverse transcription-polymerase chain reaction, and IFNLR1 immunoreactivity was examined by confocal microscopy. Results IFNL1 and IFNL3 mRNA levels in the uterus and vagina in normal rhesus macaques were below the measurement threshold, but mRNA levels of IFNLR1 and its variant lacking exon 6 could be readily detected. IFNLR1 immunoreactivity was primarily detected in the covering or glandular epithelia of the uterus and vagina. IFNL1 and IFNL3 mRNA levels were increased in some SHIV/ SIV-infected macaques, while mRNA levels of IFNLR1 were unchanged and mRNA levels of IFN-stimulated genes ( Mx1, Mx2, and OAS) were significantly increased. Conclusions These data indicate that the type Ⅲ IFN system is expressed in the reproductive tract of rhesus macaques, as in humans, thus providing a scientific basis for the use of rhesus macaques in studies of human infectious diseases, such as AIDS.