Hypothesis of phenotype matching and association are the most likely mechanisms in kin recognition. These hypotheses were tested by observing behavioral responses of cross-fostered root voles to urine cues from familiar and unfamiliar kin and non-kin. In experiment I, approach latency by males was significantly longer in response to non-sibling reared together (NSRT) than to non-sibling reared apart (NSRA) females, whereas, investigatory and sniffing time were significantly less in response to NSRT than to NSRA. However females showed no event bias to odors from NSRT and NSRA males. In experiment II, the behavioral responses of males and females to urine odors from siblings reared apart (SRA) and NSRA were not related to the degree of genetic relationship. It was concluded that: Association mechanism is used by male root voles in opposite-sex sibling recognition; Female voles possibly adopt multiple recognition mechanisms in different social tests.