Aldosterone (Aldo) is produced in the adrenal cortex, and plays an important role in regulating salt and water balance in the body. Studies in human and other species have suggested de novo synthesis of Aldo in the ovary. In this study, we investigated follicular levels of Aldo and expression of genes responsible for Aldo synthesis and reception in bovine follicles and CL collected from Holstein x Japanese Black heifers. Follicles and CL were classified according to the size and physiological status, or the stage of luteal development. Levels of Aldo in the follicular fluid were measured using EIA. RNA was extracted from granulosa cells (GC), theca layer (TL) and luteal tissues and subjected to a real-time PCR to quantify expression of enzymes responsible for Aldo synthesis, CYP21A2 and CYP11B1, and mineralocorticoid receptor (MR). Aldo levels in the follicles were about 100 pg/mL and 100 times less than its precursor, progesterone (P4). Aldo levels were not significantly different between healthy and atretic follicles despite the significant difference in P4 levels. CYP21A2 and MR were expressed in TL and GC. No significant difference was found among follicular classes. CYP11B1 was undetected in most of these samples. In CL, CYP21A2 and MR were expressed and their expression increased at the mid luteal phase. The expression of CYP11B1 did not differ among luteal stages. In conclusion, Aldo is not likely to be produced in the bovine ovary but the expression of the CYP21A2 suggests a possible conversion of P4 to 11-deoxycorticosterone, a weak mineralocorticoid and the precursor of Aldo. The presence of Aldo and the expression of MR suggests a possible action of Aldo in the bovine ovary.