Intensification of the agricultural production has lead to changes in landscape structure and composition of the ecosystem. In order to assess the effect of set aside on wood mouse(Apodemus sylvaticus)population dynamics, we had used a mark and recapture method to study a wood mouse population from November 2003 to December 2004 in the set aside area in Belp in northern Switzerland. The population dynamics of the wood mouse shows a seasonal fluctuation the population of wood mice increased in the autumn or winter to a peak and declined to a trough in the summer. We considered that the main reason for this result was habitat quality. In the set aside area, vegetation coverage is high, food resource are plentiful and varied, and there is less human disturbance. These advantages are responsible for the movement of the wood mouse living in the farmland to the set aside area. The ploughing of farmland has worsened the habitat quality for wood mouse in the farmland, thus the wood mouse was forced to move into the set aside area, and the population density increased. In the set aside, recapture rate of wood mice is low, but recruitment into the population is high. There was a significant difference in body weight between the sexes among common voles. Intensification of the agricultural production has lead to changes in landscape structure and composition of the ecosystem. In order to assess the effect of set aside on wood mouse (Apodemus sylvaticus) population dynamics, we had used a mark and recapture method to study a wood mouse population from November 2003 to December 2004 in the set aside area in Belp in northern Switzerland. The population dynamics of the wood mouse shows a seasonal fluctuation the population of wood mice increased in the autumn or winter to a peak and declined to a trough in the We considered that the main reason for this result was habitat quality. In the set aside area, vegetation coverage is high, food resource are plentiful and varied, and there is less human disturbance. These advantages are responsible for the movement of the wood. mouse living in the farmland to the set aside area. The plowing of farmland has worsened the habitat quality for wood mouse in the farmland, thus the wood mouse was f In the set aside, recapture rate of wood mice is low, but recruitment into the population is high. There was a significant difference in body weight between the sexes among common voles .