Abstract Female bank voles suppress their reproduction when the risk of small mustelid predation is high. The mechanism for this reproductive suppression is unknown. Because rodents are known to alter their oestrous cycle in response to changing environmental conditions, the effect of predation risk on the oestrous cycle of bank vole females was studied. The oestrous cycles of 24 females divided into two treatments (predation risk and control) were observed for 20 days using female receptivity as an indication of oestrus. Voles exposed for 2–3 h a day for 20 days to the close presence of a least weasel, Mustela nivalis nivalis, had fewer oestrous cycles than control females exposed to a domestic rabbit, Oryctolagus cuniculus. Females under predation risk had more abnormally long cycles than did control females. The number of days females were in oestrus tended to be lower in the predator-exposure group than in the control group. For those females that performed lordosis, the latency to lordosis did not differ between treatments. The amount of food consumed or weight change in females did not differ between treatments. The results indicate that female bank voles may respond to predation risk by suppressing their oestrous cycle. Suppressed oestrus may be a mechanism for the breeding suppression observed under the risk of small mustelid predation in female voles. Whether females suppressing oestrus have selective advantage in terms of future survival requires further study.