Metal N-heterocyclic carbene (NHC) complexes have attracted considerable attention in biological fields for their potential applications in cancer and antimicrobial therapies. In this study, four new benzimidazole-based N-heterocyclic carbene salts (la-d) and their silver (I) complexes (2a-d) were synthesized. All new compounds were characterized by elemental analysis, FT-IR, H-1 NMR and, C-13 NMR spectroscopy. Additionally, single crystal structural studies for complex 2d show that the benzene rings (C9-C14) and the central benzimidazole ring system make dihedral angles of 83.58(13)degrees. The Ag-Cl and Ag-C single bond lengths are 2.3267(8) and 2.087(3) angstrom, respectively. The C-Ag-Cl bond angle is 175.20(7)degrees. The prop-1-ene moiety attached at the second N-atom of benzimidazole is disordered at two set of sites with an occupancy ratio of 0.592(6): 0.408(6). There is one intramolecular hydrogen bond interaction between C22A-H22A... N2. The salts and Ag-complexes were further evaluated for their in vitro anticancer activities against DU-145 human prostate cancer cells, MCF-7, MDA-MB-231 human breast cancer cells and L-929 non-cancer cell for 24 h, 48 h and 72 h using the MTT assay. The Ag(I)-NHC complexes (2a-d) showed a dose and time-dependent cytotoxic activity against all cell lines. The IC(50)s for all Ag(I) NHC complexes lower than 1 mu M for 72 h time points on cancer cells. The results showed that complex 2d exhibited the highest activity against all cancer cell lines studied. Further, the complexes had relatively higher cytotoxicity to cancer cells than to non-cancer cell lines. (C) 2018 Elsevier B.V. All rights reserved.