The tensile property of roots is an important factor for anchorage and for resistance to root lodging. In this study, a root tensile test was applied to maize (Zea mays L.) grown in the field at three planting densities, 4.5 × 10⁴, 6.75 × 10⁴ and 9.0 × 10⁴ plants ha^–1, to quantify the maximum tensile force (F_max) and tensile strength (T_s) of roots at the V10 stage (tenth leaf visible) and grain-filling stage. In addition, relationships among tensile properties, diameter and turgid weight : dry weight (TW : DW) ratio of roots were investigated. The results showed that the F_max of primary and seminal adventitious roots was lower than of nodal roots. Among nodal roots, the F_max of roots on upper nodes was higher. Planting density significantly affected the tensile force of nodal roots of the sixth to eighth tiers; their F_max decreased with increasing planting density. A positive linear correlation between F_max and root diameter and a power function between T_s and root diameter was observed. In addition, there was a positive linear correlation between the TW/DW ratio and root diameter and a negative exponential correlation between T_s and TW : DW ratio. Therefore, nodal roots with a lower TW : DW ratio could have a larger T_s, because their cells are smaller and cell walls are thicker. This result suggests that nodal roots with small and thick cells benefit the tensile properties of maize.