The survival of captive-reared pheasants in the wild depends primarily on their ability to avoid predators, therefore, pheasants need to maintain their innate anti-predatory behaviour. The aim of this study was to assess the effects of age and disturbance on tonic immobility (TI) in pheasants (Phasianus colchicus) kept in a commercial rearing facility. TI tests were performed in pheasants aged 8, 10, 12, 14 and 16 weeks. Randomly selected pheasants of the same age were tested either immediately after capture (group C) or after exposure to various stimuli/disturbance (group D). No significant differences in the number of attempts to induce TI were found between the observed groups of pheasants (the vast majority of pheasants remained immobile on the first attempt). The effect of age was found only in group D, where birds aged 14 and 16 weeks showed a reduction in the duration of TI compared to younger birds. In group C, the duration of TI in pheasants of different ages did not differ. The results document a change in the duration of TI in response to an intense stimulus depending on the age of captive-reared pheasants. Knowledge of changes in anti-predatory behaviour depending on age and habituation to the environment and new stimuli is essential when determining the optimal age for pheasants to be released into the wild considering its impact on the subsequent survival of the released birds. Birds released at an older age and thus accustomed to repeated disturbances during captive rearing may have impaired defence behaviour.