The aim of the study was to develop prediction equations for assessing, in vivo, the whole body composition of growing rabbits. The accuracy of the models obtained was externally validated with independent data sets. One hundred fifty rabbits grouped at 5 different ages (25, 35, 49, 63, and 77 d) were used. A body composition analyzer with 4 terminals was used to obtain resistance (Rs; Ω) and reactance (Xc; Ω) values. The distance between internal electrodes (D; cm), body length (Len; cm), and live BW (g) were also registered. Average values of Rs, Xc, impedance (Z), Len, D, and BW were 83.5 ± 23.1 Ω, 18.2 ± 3.8 Ω, 85.6 ± 22.9 Ω, 30.6 ± 6.9 cm, 10.8 ± 3.1 cm, and 1,454 ± 845 g, respectively. At each selected age, animals were slaughtered, ground, and frozen (-20°C) for determining water, fat, CP, ash, and GE (70.5 ± 3.36%, 27.7 ± 7.61% DM, 54.9 ± 5.41% DM, 11.1 ± 1.55% DM, and 2,267 ± 183 kJ/100 g DM, on average, respectively). Fat and GE contents increased with the age, whereas CP, ash, and water contents decreased. A multiple linear regression analysis was used to determine the prediction equations, using BW, Len, and Z data as independent variables. Equations obtained to estimate water (g), CP (g), fat (g), ash (g), and GE (MJ) had coefficient of determination () values of 0.99, 0.99, 0.97, 0.98, and 0.99, respectively, and the relative mean prediction error (RMPE) was 2.79, 6.15, 24.3, 15.2, and 10.6%, respectively. When water was expressed as a percentage, the and RMPE were 0.85 and 2.30%, respectively. When prediction of the content of protein (% DM), fat (% DM), ash (% DM), and energy (kJ/100 g DM) was done, values of 0.79, 0.83, 0.71, and 0.86, respectively, for and 5.04, 18.9, 12.0, and 3.19%, respectively, for RMPE were obtained. It could be concluded that bioelectrical impedance analysis is a good, noninvasive method to estimate, in vivo, whole body composition of growing rabbits from 25 to 77 d of age.