Urine is a major source of mammalian chemosignals. Among rodents, the sexual attractiveness and chemical constituents of urine vary with different reproductive stages. We confirmed the differing sexual attractiveness to males of the urine of lactating and non-lactating female root voles (Microtus oeconomus) and analyzed individual coding forms and lactation-specific putative pheromones, using gas chromatography-mass spectrometry (GC-MS). First, we documented the behavioral preference of male voles to urine odors of lactating and non-lactating females in a choice maze. The results showed that male voles engaged in more sniffing behavior and spent more time self-grooming in response to urinary odors of lactating females than to urinary odors of non-lactating females. We then used GC-MS to analyze the urine.s individual coding forms and potential chemosignals. We identified 34 volatile compounds, corresponding to 34 GC peaks, in the urine of female voles. The components identified in the urine samples included benzo- forms, alkanes, alkenes, acids, esters, pyrans, alcohols, and other volatile compounds. 12 basic volatiles were detected in all urine samples while others were specific to individuals. (E)5-octadecene and (N) hexadecanoic acid were specific to the lactating stage. A quantitative comparison of the relative abundances of the basic GC peaks showed no difference between the lactating and non-lactating stages, suggesting that individual identity is coded in digital form. We suggest that the urine of lactating females possesses stronger sexual attraction cues because of the presence of (E)5-octadecene and (N)hexadecanoic acid, which are putative lactating pheromones. However, the specific function of the pheromones should be assessed further by bioassay.