In the design of new strategies for the treatment of osteoporosis, noninvasive, precise, and sensitive bone mass measurement capable of detecting changes over short periods of time in small animals is essential. Most of the models described thus far require the sacrifice of the animals and/or display low reproducibility. Using a dual-energy x-ray absorptiometer (DEXA; Hologic QDR-1000) in an ultrahigh-resolution mode, we measured bone mineral density (BMD) in rats at the levels of lumbar spine (L1–4), proximal tail (caudal vertebrae C2–4), and tibia. Accuracy was evaluated by measuring the mineral content of bone powder capsules (within the range of rat vertebrae BMD), under 0.5–3 cm water to mimic variations in soft tissue thickness. The bone powder capsule mineral content was highly correlated with chemically determined hydroxyapatite content (r = 0.999). In vivo reproducibility was evaluated by calculating the coefficient of variation (CV = 100 × SD/mean) of four to six BMD measurements, each time with repositioning, in seven rats (220–500 g body weight). CV was 1.36 ± 0.32% (x ± SD) for lumbar spine, 0.66 ± 0.50% for proximal tail, and 1.12 ± 0.45% for tibia. The ability to detect BMD changes was investigated by measuring BMD before and every 4 weeks after ovariectomy (OVX) in 270 g rats, pair fed during the whole experiment. Compared with sham-operated control animals, a highly significant difference in lumbar spine BMD was observed 4 weeks after OVX, which reached a maximum by 8 weeks and remained stable thereafter. At the level of the proximal tibia, the difference was maximal 4 weeks after OVX. In contrast, proximal tail BMD was only slightly affected by OVX (p < 0.05). In conclusion, BMD measurements by noninvasive DEXA is feasible in small experimental animals. It seems to be accurate and precise, allowing the detection of BMD changes over short-term periods, particularly at lumbar and peripheral sites with high trabecular bone content. This technique should be useful for the development of therapies aimed at increasing bone mass.