Coypus (Myocastor coypus) and rabbits (Oryctolagus cuniculus) are medium-sized herbivore animals with similar morphological features of the digestive tract. Comparative nutritional trials with coypus and rabbits are scarce. In this study, weights of digestive organs and some parameters of their contents were determined in coypus and rabbits fed the same diet ad libitum. In conclusion, there are both differences and similarities in parameters of digestion in both animal species. Caecal fermentation pattern differed more than other parameters investigated.