Adult skin and fetal fibroblasts are the most frequently used donor cell types for bovine cloning by nuclear transfer (NT) but there are few reports concerning Nelore cattle. The aim of this study was to evaluate in vitro and in vivo viability of Nelore nuclear transfer embryos reconstructed with Metaphase II oocytes and differentiated somatic cells (adult ear and fetal fibroblasts). Oocytes from ovaries collected at slaughterhouse were matured in vitro for 17 h. Enucleation was conducted by aspiration of the first polar body (PB) and small volume of cytoplasm containing metaphase plate. For NT, each nucleus donor cell was inserted under the zona pellucida of each enucleated oocyte and the enucleated oocyte-nuclei donor cell complexes were electrofused (2 pulses of 4 KV cm^-1 for 20 s). After electrical activation, the couplets were incubated in TCM199 plus 7.5% FCS supplemented with cycloheximide (10 g mL^-1) and cytochalasin D (2.5 g mL^-1) for 1 h and ciclohexemide alone for 4 additional hours. Immediately after activation, reconstructed embryos were co-cultured with granulosa cells in SOF + 5% FCS for 7–9 days. At 7th day of culture, some blastocysts were fixed for counting cells and some transferred into recipients. A total of 377 couplets were reconstructed from fetal and 457 from adult fibroblasts. After electrofusion, 138 (fetal cells) and 166 (adult cells) embryos were incubated, and 24 (17.4%) and 26 (15.7%) reached blastocyst stage, respectively. The blastocyst cell number means were 101.3, 120 and 114.3, respectively, for adult, fetal and IVF (control) embryos. There were no significant differences in the numbers of cells of blastocysts among the groups. After transferring 18 (fetal cells) and 21 (adult cells) blastocysts, pregnancy rates at day 90 were 16.7% (3) and 19% (4). There were no significant differences between pregnancy rates. The first pregnancy from fetal cells delivered a healthy male calf weighing 34 kg at Day 290. One of the remaining recipients died with hydrallantois at Day 229 and the other aborted at Day 252. There are four 5-month-pregnancies of adult fibroblast reconstructed embryos. These results indicate that NT embryos produced by fetal and adult fibroblasts of Nelore breed show similar rates of in vitro and in vivo developments. This work was supported by FAPESP (99/07377-3).