The mole rat (Spalax ehrenbergi) is a blind, solitary, highly aggressive subterranean rodent well adapted to underground life, and in Israel involves four chromosomal species (Nevo, 1991). Little is known to date about its reproductive biology and all attempts to breed mole rats in captivity have failed. The present study investigated the effects of three different light regimes on vaginal smear and annual cycle of body weight, age at sexual maturity, and various parameters of reproductive behaviour of female mole rats. Daily vaginal smears throughout the year revealed that the mole rat does not have a regular oestrous cycle, but exhibits an annual rhythm with a seasonally cornified smear. Regardless of the photoperiods the females were exposed to in the laboratory, relatively high proportions of cornified smears were found during the winter breeding season. A second, albeit small, peak of cornified cells was found during the summer season. Photoperiod had no effect on annual body mass cycle either, and mole rats kept under the different lighting regimes reached their maximum weight just prior to the beginning of the breeding season. In young females, vaginal opening occurs at the age of four weeks and first cornified smear at the age of 4–7 months. The presence of a cornified smear was found to be an insufficient criterion for receptivity, but providing the opportunity for a female to choose her mate enhances the chances of copulations occurring during encounters. We conclude that the mole rat is a seasonal breeder which reproduces during the winter, but has the potential of summer breeding too. Our findings also suggest that females probably have the potential to breed in their first winter. The seasonally constant vaginal smear periods, and the post copulation vaginal smear data are the first evidence suggesting that the mole rat is a reflex ovulator, but the ovulatory failure we observed after single copulations raises the possibility that multiple copulations are necessary to induce ovulation.