Designing and application of composites based on nanodiamonds and biodegradable polyhydroxyalkanoates are discussed. As an example, 3-polyhydroxybutyrate (PHB) microspheres - modified detonation nanodiamonds (MDND) composite was obtained by the bimolecular nucleophilic addition reaction (Ad_N2 type). It is shown that at acid pH from 70 up to 150 mg MDND can be immobilized on 1 mg of biopolymer microspheres depending on the weight ratio of the components.