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Nb(2)AsC showed superior mechanical properties to those of other layered ternary carbides (Kumar et al 2005 Appl. Phys. Lett. 86 111904). In the present density functional calculation, the underlying mechanism is interpreted by astonishing bonding features of Nb(2)AsC. The Nb d-As (p(x) + p(y)) and Nb d-As p(z) bonding states locate in the same energy range as those of Nb d-C p bonding, which indicates that the Nb-As bond has similar bonding strength as the Nb-C bond does; and thereafter, Nb(2)AsC has improved mechanical properties compared to the others. The present reported bonding features are interestingly different from those experienced by T(2)AlC (T=Ti, V, Cr, and Nb), wherein the weak T-Al coupling was separated from T-C bonding states in the higher energy level by a pseudogap. This work proposes an effective method to strengthen the relative weaker T-A (A is the A-group element) bonding in layered ternary carbides.