The purpose of this study was to compare the Rudolph J. Liedtke (RJL) Sciences Quantum II system bioelectrical impedance analyzer (BIA) with the fan beam Hologic dual-energy X-ray absorptiometry (DXA, software V8.26a) for assessing body composition in postmenopausal obese women. Thirty-three postmenopausal overweight/obese females (mean age: 53.9+/-6.0 yr; mean weight: 91.3+/-17.5 kg; and mean body mass index [BMI]: 33.1+/-5.7 kg/m2) were evaluated for comparison of body weight (BW), fat mass (FM), percent FM (%FM), and fat free mass (FFM). The comparison was assessed by RJL Quantum 2 Cyprus 2.6 (Clinton Township, MI) BIA vs fan beam DXA Hologic QDR-4500A software V8.26a (ODR 4500 Hologic, Inc., Waltham, Mass). RJL-BIA and DXA measurements were performed at the same time. BW was measured using a balance scale (Detecto; Web City, MO) and these results were used for the RJL-BIA analysis. Balance weight was compared with DXA BW. Correlations between DXA and RJL-BIA for BW, FM, %FM, and FFM were 0.998, 0.980, 0.782, and 0.926 (p<0.01), respectively. Bland-Altman plots demonstrated general agreement between methods for BW, FM, %FM, and FFM. However, for the latter 3 metrics of body composition, one unit change using BIA does not correspond to one unit change using DXA, as there were systematic disagreements at either end of the range of values. But RJL-BIA could be a valid method for assessing body composition of overweight/obese postmenopausal women once appropriate validated regression equations have been developed.