his study hypothesized that heat and cold stress affect the balance between oxidants and antioxidants (oxidative stress) of oocytes and follicular fluid (FF) in beef cattle and the oxidative stress between blood and FF is correlated. Thirty-two Japanese Black cattle that were divided into four seasonal groups [fall, winter (WG), spring (SpG), and summer (SmG) group]. Plasma and FF were measured diacron-reactive oxygen metabolites (d-ROMs), biological antioxidant potential (BAP), and oxidative stress index (OSI). Reactive oxygen species (ROS) were measured in oocytes. Temperature-humidity index was lower in WG and higher in SmG than in the other three groups (P< 0.05). d-ROMs value was lower in FF than in plasma in all groups, BAP value was lower in FF than in plasma in WG, SpG, and SmG, and OSI was lower in FF than in plasma in WG and SpG (P< 0.05). In FF, d-ROMs and BAP values were positively correlated in WG, SpG, and heifer groups (HG, P< 0.05). d-ROMs or OSI values between plasma and FF were positively correlated in all animals and cow group (CG), SpG, CG, and HG (P< 0.05). ROS levels in oocytes were higher in WG and SpG than in SmG (P< 0.05). In conclusion, oxidative stress in the blood and FF are linked, and oxidative stress of oocytes increases in winter and spring in beef cattle that are kept on pasture, except in winter.