The aim of this experiment was to study the effect of maturity stage of grass at harvest on particle size in faeces from ewes fed grass silage ad libitum. Eighteen pregnant Swedish ewes bearing two foetuses were given one of three treatments as their only feed. The treatments were early (ECS), medium (MCS) or late (LCS) cut grass silage. The ECS, MCS and LCS silages contained 449, 578, and 634 g NDF kg^-1 and 166, 111 and 81 g crude protein kg^-1 DM, respectively. The in situ rumen indigestible NDF (INDF) was 77, 164 and 268 g kg^-1 of NDF; the degradation rate of digestible NDF (k_dDNDF) was 64, 47 and 44 g kg^-1 h^-1 and DM intake was 2.5, 2.1 and 1.5 kg d^-1 for ECS, MCS and LCS silage, respectively. Faeces samples were collected during four days, washed in nylon bags, freeze dried and sieved into six sieving fractions; bottom bowl (B), 0.106 (C), 0.212 (D), 0.5 (S), 1.0 (M) and 2.36 (O) mm pore size. The proportions of particles in the B, C, D, S and O fractions were affected by cutting time of the silaage (P < 0.003). In conclusion, stage of maturity at harvest strongly affects the distribution of particle size in faeces from ewes fed grass silages.