Some epidemiological studies have suggested that exposure to extremely low‐frequency magnetic fields (ELF‐MFs) can affect the immune system. This study aimed to investigate the effects of antioxidant vitamin consumption on proinflammatory cytokines and biochemical parameters changes. In this randomized, controlled double‐blinded trial study, power plant workers exposed to ELF‐MFs were enrolled based on inclusion criteria. Ninety‐one eligible subjects were randomly divided into four groups: the first group (400 units of vitamin E/day), second group (1,000 mg of vitamin C/day), third group (400 units of vitamin E and 1,000 mg of vitamin C/day), and control group. The intervention was conducted for 3 months. Proinflammatory cytokines interleukin‐1β (IL‐1β), IL‐6, and tumor necrosis factor‐α (TNF‐α), and biochemical parameters (fasting blood sugar, total cholesterol, triglyceride, low‐density lipoprotein cholesterol, high‐density lipoprotein cholesterol [HDL‐c], total protein, and albumin) were measured among the participants’ serums, before and after the intervention. The mean level of IL‐6 in all vitamin‐receiving groups, the mean level of IL‐1β in vitamin C and E&C groups, and the mean level of TNF‐α in the vitamin C group, decreased significantly after intervention. The arithmetic means of the effect sizes for IL‐1β, IL‐6, and TNF‐α were 0.71, 0.57, and 0.2, respectively. The level of HDL‐c in the vitamin E and vitamin E&C groups and the level of triglyceride in the vitamin C group significantly increased after the intervention. Taking antioxidant vitamins can prevent an increase of proinflammatory cytokines induced by prolonged exposure to ELF‐MFs. Bioelectromagnetics. 2021;42:18–26. © 2020 Bioelectromagnetics Society