Abstract:The relationship between root growth and tolerance to phosphorus (P) deficiency in maize (Zea mays L.) seedlings was investigated by using two P - efficient (181 and 186) and two P - inefficient (153 and 197) inbred lines which were selected based on the previous field experiment. The shoot biomass, biomass of primary roots and secondary roots, and P content of all the genotypes were reduced at P deficiency (P 5.78 mg/kg soil). However, the P - efficient lines 181 and 186 were less affected. Up to 6 - leaf age of maize, the number of primary and secondary roots of all the genotypes were merely affected. Two lines, 181 and 197, were selected to investigate the root morphology further. It was found that both the lateral and axile roots of 197 decreased drastically with P stress, while those of 181 were not. At P deficiency, the ratio of lateral roots to axile roots, root length to root weight of the primary roots of 181 increased significantly. It was supposed that the allocation of nutrients and dry matter in roots of 181 was more in favor of fine roots so that its total root length was maintained .