PURPOSE: The aim of this study was to analyze the changes that occur in rats with experimental endometriosis after treatment with copaiba oil. METHODS: Experimental endometriosis was induced in rats. The experimental group received copaiba oil (Copaiferalangsdorffii) orally (0.63 mg/day), and the control group received a 0.9% sodium chloride solution orally (1 ml/100 g of body weight/day). Both groups were treated with gavage for 14 days. After this period, the animals were euthanized, and the implant volume was calculated. The autologous transplants were removed, dyed with hematoxylin-eosin, and analyzed by light microscopy. RESULTS: The average final volumes were significantly different between the groups (p=0.007). There was a significant increase (p=0.012) between the initial and final volumes in the control group, whereas treatment with Copaiferalangsdorffii caused a marked reduction in endometrial growth over time (p=0.016). Histologically, 6/11 (55.00%) rats in the experimental group had a well-preserved epithelial layer, and 3 (45.00%) had mildly preserved epithelium. The control group had seven cases (58.30%) of well-preserved epithelial cells and five cases (41.70%) of mildly preserved epithelial cells (p>0.05). CONCLUSION: Copaiba oil (Copaiferalangsdorffii) appears to be a promising alternative treatment for endometriosis.