A 25Cr-20Ni austenitic steel containing 0.59 wt % nitrogen was aged at 973, 1023, 1073 and 1123K to study the growth features of the cellular precipitation of Cr₂N. Experimentally determined were volume fraction of the cell, averge migration rate of cell boundaries, and averge concentration of nitrogen in the untransformed matrix. The partitioning of nitrogen between the cell and the untransformed matrix was computed on the basis of those data. The average concentration of nitrogen within the cell is higher than initial concentration of nitrogen at the onset of the cellular reaction. It decreases linearly with the increasing volume friction of cell and its gradient increases as the aging temperature decreases. At a given aging temperature, it is determined by the average concentration of nitrogen in the untransformed matrix, irrespective of the initial concentration of nitrogen.