The complexes [(η5-C5H4–CO–R)Mo(CO)2(η3-C3H5)] [R = OH (1), Phe–OMe (2)] have been examined as guests for the cyclodextrin (CD) hosts β-CD and heptakis(2,3,6-tri-O-methyl)-β-CD (TRIMEB), and the resultant inclusion compounds have been characterised in the solid state by elemental and thermogravimetric analyses, powder X-ray diffraction, 13C{1H} cross-polarisation (CP) magic angle spinning (MAS) NMR spectroscopy and FTIR spectroscopy. Single-crystal X-ray analysis of 1 shows that the unit cell contains centrosymmetric supramolecular dimers comprising two dicarbonyl complexes linked through hydrogen-bonding interactions involving the carboxylic acid groups. In screening tests for antiproliferative effects, the CD adducts containing 1 displayed enhanced antitumour activity against mouse melanoma (when compared with nonincluded 1), while showing minimal activity towards human adenocarcinoma and nontumour rat myoblast cell lines. TRIMEB encapsulation resulted in a predominant toxic effect on tumour cells versus the non-neoplastic myoblast cells.