This study investigates the flow properties of binary mixtures of both commercial ibuprofen and reprocessed ibuprofen through high shear milling with lactose powders. Ibuprofen is recrystallized in a 30% water-ethanol mixture before high shear wet milling (HSWM). In-situ Process Analytical Techniques (PAT) (Labmax (R)) is used to study the HSWM process dynamics, with particle size measured by a Lasentec Focused Beam Reflectance Measurement, FBRM (R). The flow properties of the binary mixtures of the different ibuprofen particles and its binary mixtures with lactose were measured using a Schulze (R) RST-XS ring shear tester. Results show that the morphology of ibuprofen was changed from needle to hexagonal like crystals during recrystallization and crystal size was reduced dramatically by HSWM for 1 h. The flowability of milled ibuprofen powders is reduced significantly due to its reduced size and change of surface morphology. Mixing the HSWM ibuprofen powders with lactose enhanced its flow properties. However, the increase of the mixture flowability for HSWM ibuprofen is less significant in comparison to the binary mixtures of lactose with commercial ibuprofen. (C) 2012 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan. All rights reserved.