This paper deals with the problem of dendritic sidebranches in binary system. The solution of dendritic interface corresponding to a global neutral mode is given. Changing relationships of the distance from dendritic tip to sidebranch-tip, the sidebranch spacing and amplitude with undercooling and impurity concentration are presented using numerical calculation. The results show that all of the distance from dendritic tip to sidebranch-tip, the sidebranch spacing and amplitude scaled by the radius of dendritic tip decrease as undercooling increases. For the fixed undercooling, changes of the scaled distance, spacing and amplitude are more obvious in the region of the small solute concentration. However, the dependence of the scaled distance, spacing and amplitude on both of undercooling and impurity concentration is very weak. The predicted results are agreement with the experimental observation for the pure materials.