Dicyclohexyltin derivatives Cy,SnL(Cy = cyclohexyl) of the dipeptides H,L, glycylglycine, glycylalanine, alanylglycine, glycylvaline, glycylmethionine, glycylphenylalanine and glycyltyrosine, have been obtained by neutralization of Cy,SnO and H,L.The crystal structures of Cy,SnL (L = glycylglycinate, glycylalaninate) have been determined by single X-ray diffraction. Tin in each case has a distorted trigonal bipyramidal environment with the dipeptide acting as a tridentate NNO-ligand. From IR-data, and in some cases from '19Sn Mossbauer and '19Sn NMR data, analogous molecular structures are inferred for the other compounds Cy,SnL. Spectroscopic data indicate that the solid-state structures are retained in organic solvents.In oitro tests showed Cy,SnL (H,L= glycylglycine, glycylalanine, alanylglycine, glycylphenylalanine, glycyltyrosine) to exhibit high cytotoxicity against MDA/MB 231 breast cancer cells, while Me,SnL (L = glycylalaninate, glycyltyrosinate, glycyltryptophanate), and R,Snglycylglycinate (R = n-Bu, Ph) proved to be much less active.