In this work, we have quantified effects of moisture content, over the relative humidity (RH) range of 5–92% corresponding to 1.6–10.9% of water content, on flow properties of a grade of microcrystalline cellulose (Avicel PH102) using a ring shear cell. Several key powder flow parameters, including cohesion (τc), unconfined yield strength (fc), powder bulk density (ρb), flowability (ffc), and effective angle of internal friction (ϕe), were assessed.