The aims of the present study were to detect the ontogeny of estrogen receptor (ERalpha and ERbeta) and androgen receptor (AR) expressions and their co-localization with Islet-1 in the developing dorsal root ganglia (DRG) of sheep fetuses by immunohistochemistry. From the single staining results, the ERalpha immunoreactivity (ERalpha-ir), ERbeta immunoreactivity (ERbeta-ir) and AR immunoreactivity (AR-ir) was first detected at days 90, 120 and 90 of gestation, respectively. From days 90 to 120, ERalpha and AR were consistently detected in the nuclei of DRG neurons and the relative percentage (approximately 60%) of ERalpha-ir or AR-ir cells did not change significantly. Moreover, there was no change in ERalpha expression, while a dramatic loss of AR expression was observed at birth. From day 120 of gestation to birth, very few neurons (approximately 8%) showed nuclear ERbeta immunoreactivity. The dual staining results showed that Islet-1 was co-localized with ERalpha, ERbeta or AR in the nuclei of DRG neurons with various frequencies, and over 70% ERalpha-ir, ERbeta-ir or AR-ir cells contained Islet-1. These results imply that ERs, AR and Islet-1 may be important in regulating the differentiation and functional maintenance of some phenotypes of DRG neurons after mid-gestation in the sheep fetus.