The present communication reports the results of application of stable hybrid solid dispersed phase-based (nanodiamonds-nanosilica/titania) suspensions in cytotoxicity tests, using two different cell lines – the mouse sarcoma (J774.G8) and the ovarian carcinoma (OVCAR 8). It is also demonstrated that binary (1 wt% of nanodiamonds and 5 wt% of nanosilica/titania) suspension is more stable than individually prepared (nanodiamonds alone) in normal saline solution (0.9 wt% NaCl). With the help of scanning electron microscopy the structure and the morphology of hybrid aggregate particles in dried suspensions (xerogels) were examined. In normal saline solution the subject suspensions do not experience the sedimentation by dilution within 24 h after addition of identical dispersion medium, while the negative zeta-potential (−28.8 mV) decreases to zero (4- times dilution) and the solid phase is characterized by aggregates size at ≤160 nm from the DLS measurements. The tests of biocompatibility (cytotoxicity) did not demonstrate any statistically significant toxicity at the suspension in the concentrations range of 0.01–0.155% (in respect to nanodiamonds in the suspensions diluted by cell culture, wt./vol) of the suspensions.