Circadian activity patterns of three giant pandas were monitored using GPS collars equipped with dual-axis activity sensors during the spring umbrella bamboo growing season in Wolong Nature Reserve. We summarized activity rate (% of time active) and level (horizontal direction/ vertical direction ranging from 0 to 255) across different times of day and across individuals and compared activity level to both solar radiation and air temperature. The results showed that the mean activity rate of the pandas was 68.05%. Activity rate (70.86%) and level of the pregnant panda (23.82±0.30/ 17.63±0.22) was higher than the other two (70.55%, 14.71±0.17/ 13.52±0.15 and 62.76%, 17.74±0.23/ 13.61±0.18). There were three activity peaks at 6:00-7:00, 18:00-21:00 and 23:00-3:00, and a marked rest period at 9:00-12:00. Activity rate (68.32%) and level during the day (19.59±0.20/ 15.45±0.15) was higher than in the night (67.67%,17.63±0.19/ 14.21±0.15). The effect of solar radiation was significantly negatively and linearly related to the daily activity level of the study pandas (r=-0.822, P<0.001), however, the air temperature was not linearly related to circadian activity level.