The synthesis and in vitro anticancer activity of OsII-arene complexes with carbohydrate-derived phosphite co-ligands are reported. The compds. were characterized by std. methods and the mol. structure of dichlorido(η6-p-cymene)(3,5,6-bicyclophosphite-1,2-O-isopropylidene-α-d-glucofuranoside)osmium(ii) was detd. by x-ray diffraction anal. Complexes with chlorido leaving groups undergo hydrolysis by consecutive formation of aqua compds., followed by cleavage of a P-O bond of sugar phosphite ligands, as demonstrated by NMR studies. These observations are similar to those of analogous RuII-arene complexes; however the rate of hydrolysis is very slow for Os compds. The complexes with oxalato leaving groups resist hydrolysis; no hydrolytic species were detected by 31P{1H} NMR spectroscopy over several days. Within this series of Os compds., in vitro anticancer activity is highest for the most lipophilic chlorido complex dichlorido(η6-p-cymene)(3,5,6-bicyclophosphite-1,2-O-cyclohexylidene-α-d-glucofuranoside)osmium(II).