The aim of the study was to analyse the influence on tail-biting in undocked pigs during the rearing period of crude fibre in piglets' rations. All pigs were fed the same pre-starter until weaning. The study comprised two trials with four experimental groups each. The first trial contained: a control group (CG1) with conventional feed (up to 40 g/kg crude fibre), two groups with an increased crude fibre content of up to 50 g/kg (G5) and 60 g/kg (G6), respectively, and one group with conventional feed and crude fibre provision ad libitum (AL). The second trial consisted of a control group (CG2) which received the same conventional feed as CG1 and three treatment groups with either soya hulls (SS), dried sugar beet pulp (DP) or oat fibre (OF) admixed to their ration, to achieve a crude fibre content of 60 g/kg in all three groups. The rearing week, the batch, the treatment group (only in trial one) and the interaction between batch and treatment group had a significant influence on tail-lesions (P < 0.05). The tail-biting process started in rearing week 3 (trial one) and 5 (trial two), respectively. Due to the low frequency of tail-biting during the present study, crude fibre seems to have no major influence on tail-biting during the rearing period. This unexpected result may be caused by the optimized conditions in which the piglets were kept and the intensive animal observation carried out by the employees. However, the batch effect was most influential.