In this study, 154 pectoralis major breast muscles from three chicken age groups were separated into different severity levels of wooden breast condition by manual palpation to investigate the changes of lipid and protein oxidation and citrate synthase activity. TBARS values, carbonyl contents and loss of free thiol groups were greater (P < 0.05) in the superficial (ventral) part of severe wooden breast samples, whereas no clear change was found in the deep (dorsal) part. Mitochondrial citrate synthase activity declined with increasing severity of wooden breast myopathy. Both bird age and wooden breast degree showed significant main effects on these indicators, while no interaction effect was observed. Moreover, there were significant correlations between lipid and protein oxidation and citrate synthase activity. Here, we propose a hypothesis that lipid and protein damages and mitochondrial dysfunction is linked to the aggravation of the wooden breast myopathy. •Increased severity of wooden breast increases lipid and protein oxidation.•Increased severity of wooden breast increases mitochondrial dysfunction.•Superficial parts of breast fillets are more vulnerable to wooden breast myopathy.•Accumulation of oxidative stress is associated with wooden breast development.