Following a request from the European Commission, the Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on the safety and efficacy of HOSTAZYM ® X as a feed additive for rabbits for fattening. HOSTAZYM ® X contains endo-1,4-beta-xylanase produced by a strain of Trichoderma citrinoviride and is available in liquid and solid formulations. It is authorised as a feed additive for chickens for fattening, turkeys for fattening, laying hens, minor poultry species for fattening and laying, weaned piglets, pigs for fattening and carps. The applicant has now requested to extend the authorisation to rabbits for fattening. The FEEDAP Panel considered that the new use of the additive would not change the previous conclusions regarding the safety for the consumer, user and environment. There are no concerns for consumer safety and no risks for the environment are expected from the use of the additive as a feed additive. Regarding the safety for the user, the additive should be considered a potential skin and eye irritant, and a potential skin and respiratory sensitiser. A subchronic oral toxicity study in rats was submitted to support the safety of the additive when administered to rabbits for fattening. The maximum safe enzyme activity in feed for the rabbits for fattening was derived from the data obtained in the subchronic oral toxicity study in rats; considering the maximum safe intake derived for rabbits from the toxicological data, the FEEDAP Panel concluded that the additive is safe for rabbits for fattening at the recommended use level. Two efficacy studies were submitted to support the efficacy of the additive; a significant effect of the additive in a relevant parameter was found in only one trial. Due to the insufficient evidence the Panel could not conclude on the efficacy of the additive in rabbits for fattening.