Reactive oxygen species have fundamental roles in reproductive functions. To comprehensively evaluate the relation between reactive oxygen species and infertility, physiological variations across the estrous cycle in healthy cows have to be known. For this purpose 25 healthy multiparous Holstein dairy cows having regular estrous cycles were used. The estrous cycles were synchronized by ovsynch protocol. Oxidant [lipid hydroperoxide (LOOH), total oxidant status (TOS), oxidative stress index (OSI)], antioxidant parameters [total antioxidant status (TAS), total free sulfhydryl groups (SH), ceruloplasmin (CP), paraoxonase-1 (PON1), arylesterase (ARE), uric acid (UA)], lipid profile and progesterone levels were assayed at estrus, metestrus, diestrus and proestrus stages of the estrous cycle in the plasma samples. The plasma levels of oxidant (LOOH, TOS and OSI) and antioxidant (TAS, SH and UA) parameters were significantly decreased during the luteal phase compared to the follicular phase (at proestrus and at estrus) of the estrous cycle. There was also a significant positive correlation between TAS and TOS. The activity of PON1 and ARE significantly increased only at diestrus. Levels of high density lipoprotein, low density lipoprotein and total cholesterol elevated during the follicular phase (estrus) and declined during the luteal phase. In conclusion, oxidant/antioxidant status and lipid profile were affected by cyclic changes. Moreover, antioxidant defense system showed adaptive response to increased oxidative activities by occurring parallel increases and it may indicate that there is a dynamic balance between oxidant and antioxidant status during the estrous cycle in healthy cows.