The purpose of this research was to study the histology and describe the microscopy findings of the epididymis epithelium of greater Rhea americana at three time periods: November 2005 (n=14), December 2006 (n= 20), and May 2007 (n= 20), to observe and compare the differences that occurred. We studied the epididymis from 54 rheas, bred in Santa Maria, Rio Grande do Sul, Brazil. The epididymis were collected during commercial slaughter and fixed in bouin. Optical microscopy was used to measure the cellular structure, types of cells, tubules, and stereological values like the epididymis epithelium diameters, lumen, thickness, and relative volume of the tissue structure. Additionally, electron microscopy was studied. In December 2006 and May 2007, the means of the epididymis tubular diameter were: 79.1 and 58.1 µm, epithelium thickness: 24.0 and 52.2 µm, and lumen diameter: 55.0 and 5.8 µm, respectively. Regarding the volumetric proportion, we reported the following values: epithelium volume 36.2 and 80.4%, lumen without spermatozoon 19.6 and 3.0%, lumen with spermatozoon 5.4 and 0.0%, interstitium 35.4 and 12.0%, blood vessels 3.5 and 4.6%, structures in cellular superficies 1.4 and 0%, lamina 1.4 and 3.2%, and artifacts 0.3 and 1.3%, respectively. The epididymis ducts had a circular form in transverse sections with spermatozoon only in November 2005 and December 2006. The Rhea’s epididymis morphology was found to be similar to ostriches, roosters, and Japanese quail. Here, we present data from stereological microscopy (tubular diameter, epithelium thickness, and lumen diameter), volumetric proportion (epithelium, lumen without spermatozoon, lumen with spermatozoon, interstitium, blood vessels, structures in cellular superficies; cilium, estereocilium, and lamina) in this species during the repose and sexual activity period (reproductive season).