The reaction of tert-butyl isocyanate (2) with the optically active cyanohydrins (R)-1a,b was accompanied with inversion of configuration giving the chiral (S)-enantiomers of the respective carbamate derivatives 3a,b. On the other hand, reactions of aryl isocyanate reagents Ar-N=C=O 5a-d with cyanohydrins (R)-1a-c gave the corresponding optically active 4-imino-2-oxazolidinone derivatives 7a-h in the form of their Sconfiguration. Moreover, the same reactions were also applied for the racemic cyanohydrins 1a-c and/or 1d to afford the corresponding carbamates (R,S)-3a,b, (R,S)-4 and/or 4-imino-2-oxazolidinones (R,S)-7b,d-h as racemic mixtures. Structures of the new products were elucidated with compatible micro analytical and spectroscopic (IR, 1H-NMR, 13C-NMR and MS) measurements. The X-ray crystallographic analysis provided an efficient tool in confirming the structure and configuration of the new chiral compounds. The antimicrobial activity of selected new derivatives against four bacterial species (Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa) and two fungi (Aspergillus flavus and Candida albicans) were evaluated. Moreover, some of the new products were screened for their in vitro antitumor activity against the human solid cancer cell lines, Human Carcinoma (HCT116), Human Hepatocellular Liver Carcinoma (HepG2) and Human Breast Adenocarcinoma (MCF-7) cell lines. Generally, most of the investigated compounds have shown moderate to high activities in comparison with the standard drugs. The structure-activity relationship (SAR) has been also discussed.