Good powder flow properties are needed for solid handling including mixing, pneumatic conveying, wet granulation, tabletting and so on. In order to obtain the desired bulk flow properties, a good selection of processing and storage conditions is required. In the past, much attention has been given to relate bulk flow with powder properties such as particle size distribution, bulk and tap density, and shape and morphology. However, very little has been done to study the influence of inter-particle interactions on bulk flow. It is the aim of this paper to investigate the link between inter-particle interactions and flow properties of powder being stored under different conditions and prepared differently. Crystalline adipic acid before and after ball milling will be stored under different humidity conditions. AFM will be used to study the friction-load dependence at single particle level while Jenike shear tester will be used to measure the bulk yield loci. The results will provide useful guideline into the selection of particle preparation method as well as storage condition to achieve the desired powder flow properties.