This work aims to investigate the aggregate size effect on changes in mineralogical composition and microstructure of lime-treated compacted soils. Three soil powders with different maximum aggregate sizes (Dmax=5, 1 and 0.4mm) were prepared prior to the treatment with 2% of lime. X-ray diffraction (XRD), environmental scanning electron microscope (Env. SEM) coupled with chemical analysis using energy dispersive X-ray spectrometry (EDX) and mercury intrusion porosimetry (MIP) were used to analyse untreated and treated samples at various curing times. Crystallized C-S-H on tobermorite form was identified in the lime-treated soil prepared with large aggregates after one year curing, and an evident increase in nanopores b0.1 ¼mC-S-H was also observed due to CS-H creation. By contrast, in the case of smaller aggregates, no obvious C-S-H peaks were observed by XRD technique after the same curing time, even though some evidence of such phases are provided by Env. SEM coupled to EDX analysis. But a large amount of undetectable nanopores b6 nm (considering the MIP technical limitation) was supposed to be formed and could be attributed to the creation of nanocrystallized C-S-H or poorly-crystallized C-S-H (that may fill the pores larger than 2 ¼m). Such type of C-S-H phases occurred when lime was coated in thin layer on the large surface associated to lime-treated soil prepared with small aggregates.