Bonding compositions for the hard tissue of the human body comprising, as the main component, (A) at least one member of polymerizable acrylate esters, methacrylate esters, acrylamide derivatives or methacrylamide derivatives possessing at least one group selected from the group consisting of a carboxyl group, epoxy group, amino group and hydroxyl group, and (B) at least one member of alkoxy-containing titanium compounds or alkoxy-containing silicon compounds.