Abstract: By the method of in situ soil coreion exchange resin bag (ISCIERB), the characteristics of soil nitrogen mineralization in the different successive rotation stands of poplar plantation (the first rotation of fouryearold and the second rotation of fouryearold) and the effects of tillage on the soil nitrogen mineralization in the second rotation of fouryearold poplar plantation were studied in north Jiangsu province. The results showed that the seasonal changes of soil ammonification rate in two rotation stands were similar. The soil ammonification rate in the second rotation stand was not obviously decreased and even increased in April and July, compared with the first rotation stand. However, the soil nitrification rate and net mineralization rate in the second rotation stand were significantly lower than that in the first rotation stand, especially in March, April and May. Compared with the notillage, the annual ammonified, nitrified and mineralized nitrogen of soil in the second rotation stand treated with the tillage were increased. Meanwhile, the tillage treatment was obviously increased the soil N lose by leaching which accounted for 49.15% of the total annual mineralized N, therefore soil inorganic N content was lower in the stand treated with tillage than that in the stand with notillage.