Abstract: Most mammalian sex determination belongs to male heterogametic type of genetic sex determination. Sex de-termination of most mammals depends on the Y chromosome. SRY gene is the testis-determining factor on Y chromosome of most mammals, which is thought to be the most important gene in sex determination by far. Recent studies on Microtus mandarinus mandarinus demonstrated that the subspecies has Y chromosome, but there is no SRY gene on Y chromosome. Sex determination of Microtus mandarinus mandarinus is independent of SRY gene. R-spondin1 has also been excluded as the sex determination gene of Microtus mandarinus mandarinus. This paper reviews recent advances on sex determining mechanisms of Microtus mandarinus mandarinus. Possible sex determining mechanisms of Microtus mandarinus mandarinus in the absence of SRY gene are also discussed.