The primary aim of the present study was to assess whether low dose vitamin C supplemented in its natural form, as a dried powder from selected subspecies of rosehip (Rosa canina), would result in a detectable increase in the concentration of blood vitamin C in horses supplemented daily for three months. In a secondary part of the study, the anti-oxidant capacity of the present treatment was also tested. Sixteen horses were randomly allocated to two groups and supplemented with either 25 g rosehip powder daily (equal to 125 mg natural vitamin C), or with 50 gram rosehip powder daily (equal to 250 mg vitamin C). Serum vitamin C was analysed both prior to supplementation and then again 14, 28 and 84 days following supplementation. Anti-oxidative capacity was assessed as the release of oxidative anions from polymorph-nucleated leucocytes prior to supplementation and after 14 and 84 days, respectively. Whilst there was a trend towards an increase in serum vitamin C concentration following 84 days of supplementation with 125 mg of natural vitamin C, this was not statistically significant. However, a significant increase in serum vitamin C concentration was observed following 14 days of supplementation with 250 mg vitamin C (P < 0.02). The magnitude of this increase was greater following 28 and 84 days of supplementation (P < 0.02 and P < 0.02), respectively. Additionally, serum vitamin C concentration was significantly higher following supplementation with 250 versus 125 mg of vitamin C daily (P < 0.03). The higher dose of natural vitamin C also resulted in a significant reduction in the release of oxidative anions (P < 0.001). These results suggest that natural vitamin C from rosehip is absorbed sufficiently to raise serum vitamin C concentration and to reduce the liberation of oxidative anions in horses supplemented with less than 500 mg daily.