Mature male Djungarian hamsters(Phodopus sungorus)were placed in individual light‐tight, sound attenuated chambers and exposed to one of four lighting conditions for a duration of approximately seven weeks. The four lighting conditions were: constant light (LL); constant dark (DD); feedback lighting (LDFB: a condition that illuminates the cage in response to locomotor activity); or a feedback lighting neighbor control (LDFBNC: the animal receives the same light pattern as a paired animal in feedback lighting, but has no control over it). Exposure of hamsters to LL or LDFBproduced significantly and similarly longer free‐running periods of the locomotor activity rhythm than exposure of animals to DD. Hamsters exposed to LDFBNCdid not free‐run or entrain, but rather displayed “relative coordination”;. The paired testes and sex accessory glands weights suggest that in the Djungarian hamster, LL and LDFBexposed animals maintained reproductive function, whereas DD exposed animals did not. Animals exposed to LDFB NChad intermediate paired testes weights. Since several previous studies have demonstrated that short pulses of light, which are coincident with the subjective night, are photostimulatory, it is not surprising that LDFBmaintained reproductive function in the mature Djungarian hamster. Feedback lighting, however, has been shown to be an insufficient stimulus to maintain reproductive function of mature male and female Syrian hamsters, and to the reproductive maturation of immature Djungarian hamsters. The results suggest that there may be slight, but significant differences in the way these two species interpret photoperiod. as well as a developmental change in the photoperiodic response of Djungarian hamsters.