During 2003–07, the moult of four captive Northern Hawk Owls Surnia ulula was studied in Poznań Zoological Garden (Poland). The aviary was under daily observation and all breeding events were recorded. It was recognized that captive conditions differ from that in the wild (food availability, expended energy — especially by males, and stress) but the study of captive owls allowed a detailed study of moult in relation to the breeding cycle of Northern Hawk Owls. Identification of dated moulted feathers enabled us to reconstruct the moult process of primaries, secondaries and rectrices. During this study the four birds had different breeding status: single, paired without breeding, paired with unsuccessful or successful breeding. In nine cases, the moult corresponded to patterns described in literature. In every case all primaries and rectrices were renewed each season. Males started moulting 3–11 days earlier than females and shed all secondaries every year while females replaced from 50–100% of secondaries annually. Rate of moult was not related to ambient temperature. During a successful breeding season, the moult of both sexes was two-phased: a short first phase with low moult intensity lasting until young owlets left the nest box followed by a longer, more intense second phase. Breeding females (egg laying and incubation) started to moult a few weeks earlier than non-breeding females but completed moult at approximately the same date. In contrast, breeding and non-breeding males had similar patterns of moulting intensity.