Background Autologous fat grafting is a common procedure performed for cosmetic and reconstructive purposes. Unpredictable graft survival is a major drawback, and a variety of improvements on technique such as using antioxidants have been reported to increase retention. The authors examined whether a natural rosemary plant extract known with antioxidant properties, rosmarinic acid, could improve the survival of the adipose tissue. Methods Inguinal fat pads were harvested from 24 Sprague Dawley rats and implanted to the parascapular area. Rats were divided into three groups: rosmarinic acid and ethanol as solvent (RA), ethanol (E), and serum physiologic (C). These substances were administered intraperitoneally daily for 1 week and once a week for 7 weeks. Volume and weight measurements, blood specimens, weight and volume records, and histopathologic examinations were performed and analyzed. Results The RA group demonstrated lower TOS, TGF-beta, TNF-alpha, and MDA values compared to E and C groups. TGF-beta increase was statistically insignificant, but TOS, TNF-alpha, MDA decrease was found statistically significant. Weight and volume losses were lower in the RA and E groups compared to the C group. The difference between the RA and E groups in terms of weight and volume loss was statistically insignificant. Histopathologically fat necrosis, inflammation, and fibrosis were less in the RA group compared to the E and C groups (p < 0.05). Conclusion Rosmarinic acid increased the fat graft volume retained and decreased cyst formation and abscess formation in the rat model. Further studies can be undertaken to investigate rosmarinic acid's local application as a tumescent and safety in humans. No Level Assigned This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors.www.springer.com/00266.