An analytical model to calculate the hardness of ultra-fine WC-10Co cemented carbides was investigated. The nanocrystalline WC-10Co powders were manufactured using a spray conversion process and sintered at 1375 degrees C in a vacuum. Varying amounts of TaC, Cr3C2, and VC were added to nanocrystalline WC-10Co cemented carbides as grain growth inhibitors. The hardness of WC-10Co cemented carbides increased with a decreasing WC grain size from 5 mu m to 300 nm. An analytical model to calculate the hardness of WC-10Co cemented carbides was proposed under the assumption that the applied load is transferred from the WC to the Co binder phase. The analytically calculated hardness showed good agreement with the experimentally measured hardness of WC-10Co cemented carbides. In the proposed analytical model, the hardness of WC-10Co cemented carbides is similar to that predicted by the Hall-Petch relationship when the WC grain size is large. However, when the grain size is finer than a critical value, the predicted hardness of the WC-10Co cemented carbide becomes saturated. (C) 2007 Elsevier B.V. All rights reserved.