Purpose.This study aimed to evaluate the effect of chronic treatment with chaetomellic acid A (CAA) on oxidative stress and renal function in a model of renal mass reduction.Methods. Male Wistar rats were subjected to 5/6 nephrectomy (RMR) or sham-operated (SO). One week after surgery, rats have been divided into four experimental groups: RMR: RMR rats without treatment(n=14); RMR + CAA: RMR rats treated with CAA(n=13); SO: SO rats without treatment(n=13); and SO + CAA: SO rats treated with CAA(n=13). CAA was intraperitoneally administered in a dose of 0.23 µg/Kg three times a week for six months.Results.RMR was accompanied by a significant reduction in catalase and glutathione reductase (GR) activity(p<0.05)and a decrease in reduced glutathione (GSH)/oxidized glutathione (GSSG) ratio. CAA administration significantly increased catalase and GR activity(p<0.05)and increased GSH/GSSG ratio, but no significant difference between the treated and nontreated groups was found in this ratio. No significant differences were found between the RMR groups in any of the parameters of renal function. However, CAA administration slightly improves some parameters of renal function.Conclusions.These data suggest that CAA could attenuate 5/6 RMR-induced oxidative stress.