We studied the diets of low-density but increasing populations of sympatric Asian elephants Elephas maximus and greater one-horned rhinoceros Rhinoceros unicornis in the Bardia National Park in lowland Nepal. A microhistological technique based on faecal material was used to estimate the seasonal diet composition of the two megaherbivores. Rhinos ate more grass than browse in all seasons, and their grass/browse ratio was significantly higher than that of elephants. Both species ate more browse in the dry season, with bark constituting an estimated 73% of the elephant diet in the cool part of that season. Diet overlap was high in the resource-rich monsoon season and lower in the resource-poor dry season, indicating partitioning of food between the two species in the period of resource limitation. Both species consumed large amounts of the floodplain grass Saccharum spontaneum, particularly during the monsoon season. As the numbers of both species increase, intraspecific and interspecific competition for S. spontaneum in the limited floodplains is likely to occur. Owing to their higher grass diet and more restricted all-year home ranges within the floodplain habitat complex, rhinos are then expected to be affected more than elephants.