Naproxen was crystallized from acetone-water in the presence of different concentrations of hydroxypropylcellulose (HPC). Naproxen particles recrystallized in the presence of HPC exhibited an obvious improvement in their packing, flow, and mechanical properties compared to naproxen recrystallized in the absence of the polymer (control particles). The results showed that the particle size distributions of the treated samples were broader than those obtained when HPC was absent. The agglomerates produced in the presence of 0.25% HPC displayed superior flow characteristics (displaying both a low angle of repose and Carr index) in comparison to samples produced in the presence of other concentrations of HPC. This was attributed to the spherical shape and smooth surface, since the area of contact in the powder bed for spherical agglomerates was smaller than that for other crystal shapes. However it was found that the tensile strength of tablets with the particles isolated in the presence of 1% HPC was increased to a greater extent than tablets produced using the spherical particles. Generally, the tensile strengths of the tablets increased with increasing concentrations of HPC present in the crystallization medium. Differential scanning calorimetry (DSC) and X-ray powder diffraction studies showed that naproxen particles, crystallized in the presence of HPC did not undergo structural modifications.