Cyclic tests were conducted to study the secant shear modulus, G\ds, of two reconstituted sands and three laboratory-made clays at small cyclic shear-strain amplitudes γ\dc≈0.0006%–0.02%. A recently developed direct simple shear device for small-strain testing was employed. The effects of cyclic strain amplitude (γ\dc), type of soil and plasticity index (PI), vertical effective consolidation stress (σ’v+c), and overconsolidation ratio (OCR) were investigated. The results show that the ordinates of the normalized shear modulus reduction curve, Gs/Gmax–γ\dc, generally increase as σ’v\dc and OCR increase. However, these effects of σ’v\dc and OCR become smaller and may eventually disappear as the PI of the soil increases.