Very few studies have addressed the systematic study on the stress-dependent behavior of cement/lime-treated structured and reconstituted soils from the viewpoint of the constrained modulus. The influence of cement/lime on the nonlinear stress-strain behavior is investigated with relation to the constrained modulus. Based on the idealized modulus-stress mode, the modulus-based parameters are defined and discussed taking into consideration cement/lime content and curing time. This contributes to establishing quantitatively the modulus-related correlations, such as ML-M0, m-ω, σ'vy-σ'r and Cc-ML on structured soils. A proposed novel concept of ΔEoed is feasible to identify the effect of soil structure, and the variation in shape and position of stress-strain curves attributes to the soil structure developed with chemical reactions. The consolidation stress at the point of ΔEoed = 0 can be considered as the yield stress, and this is proved to be appropriate in contrast to the result determined by a particular method. Comparison between structured and reconstituted soils indicates that the difference in the constrained modulus in the preyield regime is mainly caused by the existence of soil structure, and the difference of modulus in the postyield regime is closely related to an important difference in water content. Soil structure is proved to be completely destroyed from the viewpoint of material stiffness when the consolidation stress is higher than the yield stress. © 2016 American Society of Civil Engineers.