Microhardness testing was conducted on a series of TiCN-based cermets with different contents of metallic binders (5 binders, Mo?Ni=2?1) in the applied load range from 0.49 N to 9.8 N. Significant indentation size effect in the measured microhardness was observed for each test sample. Based on the energy-balance consideration, a new theoretical explanation is presented for the indentation size effect of microhardness of test sample. It is shown that only part of the work done by applied load has been transformed into the energy to cause the irreversible volume deformation of material during indentation. The extra dissipation of the work done by applied load is the main cause for decreasing tendency of microhardness with increased indentation size. The load-independent hardness was found to decrease with the increasing metallic binder content. This can be attributed to the fact that the hardnesses of metallic binders are lower than that of the TiCN matrix.