Abstract: The effect of forest patch size on reproductive success of Magpies (Pica pica) in fragmented secondaryforests was studied in Zuojia Nature Reserve and Tumenling Area of Jilin Province from 1999 to 2000.12 forest patches ranging in size from 3.5 to 46.6 hm2 were located by using GPS,and classified as large (>20 hm2,n=4),medium (10-20 hm2,n=3) and small (<10 hm2,n=5) patches.2 control samples (20 hm2) were selected in the extensive forest (>200 hm2) being contiguous to those patches.The data on breeding success,laying date,clutch size,egg weight,brood size and fledged number of the Magpies were collected in 12 patches and 2 control samples.The results show that:1)the patch size influences the reproductive success signigicantly among forest categories;2)the mean laying date in the control samples and large patches is 11.62 d earlier than that in the small ones;3)the clutch size in the control samples and large patches is bigger than that in the small ones;4)the mean weight of eggs doesnt differ between all patches and control samples,but the hatching rate and fledgeling rate are the lowest in the small patches(51.17% and 42.88% respectively),the hatching rate is the highest in the large patches (72.12%) and a little lower in the control samples (71.93%),and the fledgeling rate is the highest in the control samples (65.45%) and next in the large patches (62.71%);5)the low reproductive success of the small patches in the secondary-forests mainly caused by a high rate of nest failure.