From 26 March to 2 August 2003, both the time budget and the diurnal rhythm of behavior of breeding Black-necked Cranes (Grus nigricollis) were studied at Ruoergai Wetlands National Natural Reserve, Sichuan Province, China. The breeding season was divided into three phases: Pre-reproduction, Incubation and Chick-rearing periods. Foraging behavior was the most prevalent during the breeding season, accounting for 45% of the diurnal time budget, followed by breeding activity (28%), locomotion (10%), maintenance (9%), alert (7%), resting (1%) and “other behavior” including excretion, calling and antagonism (0.6%). During the three breeding phases, there were significant differences in the time budget of all behavior types except for locomotion and “other behavior”. In terms of frequency of events, alert behavior was the highest, occurring 43 times per hour, followed by foraging (31), maintenance (17), locomotion (11), breeding activity (5), “other behavior” (1) and resting (0.7). During the three breeding phases, there were significant differences in the frequency of various behavior types except for “other behavior”. During the day, the rhythm of different behavior types varied according to time.