The effect of γ‐radiation on polyamide fibres of PA 6, poly(ε‐caprolactam), was investigated by a viscosimetric method (unstabilized and stabilized fibres) and by the X‐ray crystal analysis (unstabilized fibres). It was found that stabilizers practically had no effect on the crosslinking and degradation processes occurring in an oxygenfree and oxygen atmosphere, respectively. The study of the degree of crystallinity and of the size of the crystallites showed that the radiation stability of the investigated fibre was relatively high.