Effect of dietary rapeseed oil from 00‐varieties of rapeseed (0, 1.5% or 3% respectively in the wet compounded diets) on plasma thyroxine (T4), reproductive performance and kit weight gain during lactation was investigated with 3 groups of each 20 mink females. Plasma T4, which has not previously been reported for female mink, was significantly lower in lactating than in non‐pregnant females. Unlike in an earlier experiment with growing male mink, it was not affected by dietary rapeseed oil. Reproductive performance, female weight development, feed consumption, and kit weight gain was normal in all treatment groups and there were no significant effects of the experimental treatment.