The in vitro gas production technique was used to observe the fermentation characteristics of three feedstuffs (barley, dried alfalfa meal, and dried beet pulp). Inocculum was provided from the caecal contents of suckling rabbits (23, 26, 31 and 35d old) which had access to their dams’ food. Mean OM degradation increased progressively with the age of the rabbits (P<0.01) from 67.4 to 70.8% with inocculum from 23 and 35d kits, and gas production from 302 to 357 ml/g OM incubated (P<0.01). It was confirmed that the in vitro gas production technique is a valid tool for the study the development of caecal microbial activity in rabbits.