The relationship between the apparent moisture content and compactibility of sodium starch glycolate was compared to similarly obtained data for pregelatinized starch. Samples of sodium starch glycolate (SSG) and pregelatinised starch (PGS) were stored at 44% or 75% relative humidity (RH), producing samples exhibiting moisture contents of up to 14% w/w, as determined by loss on drying (LOD). Increasing the moisture content of SSG and PGS resulted in an increase in compressibility and compactibility for both materials. However, the effect was more dramatic for SSG with unlubricated compactibilities of 2.0 MPa and 0.9 MPa at approximately 11.5% LOD for SSG and PGS, respectively, which was further exemplified in the compactibility of lubricated materials and in blends with microcrystalline cellulose. These results suggested that moisture content had a greater effect on the compactibility of SSG compared with PGS and that the interactions of water with the components of the SSG starch granules may be different from those within the PGS starch granules at comparable LOD values.