Carbon nanotubes (CNTs) are a promising material with excellent mechanical. electrical, chemical and thermal properties. Industries producing large quantities of CNTs typically use the fluidized bed chemical vapour deposition (CVD) technique. However, this technique presents certain challenges related to the size of CNT bundles. These challenges include agglomeration in the fluidized bed and the control of the agglomerate size distribution. Previous studies have illustrated the use of jet mills to grind CNT agglomerates. The present study tested a nozzle/target configuration to assess the feasibility of in-situ CNT grinding during synthesis in a pilot reactor. This in-situ grinding of CNTs is a new idea for which a patent is being applied. In-situ grinding of CNTs with a nozzle/target configuration is feasible at ambient conditions. The smallest volume-based arithmetic mean diameter that Could be obtained was 40 pm. The optimal target height above the nozzle tip was 0.01 m for 0.012 kg of CNTs and a 0.2 mm diameter nozzle. (C) 2008 Elsevier B.V. All rights reserved.