Electrochemical composite coatings are obtained from suspended electrolytes, in which highly dispersed powders are used as the second phase. In electro-deposition of composite coatings in electrolyte, diamond soot nanoparticles aggregation processes run actively, forming micron-sized agglomerates. Due to this, fixing the disperse phase particles on a metal matrix is complicated, which worsens the uniformity of particles distribution within the coating volume and the properties of the deposit. Therefore, we have studied diamond soot aggregation and sedimentation processes in the citrate-based copper-coating electrolyte used to obtain electrochemical composite coatings. Diamond soot content in electrolyte varies within the range of 0.2-2.0 g/l. As diamond soot, we used the detonation synthesis product manufactured by SINTA, Belarus, representing 7% water suspension. Diamond-containing soot particles consisted of super-hard and inert diamond core covered with a shell of graphite, amorphous carbon, and onion-shaped carbon. On the surfaces of the particles, there were functional groups capable of being actively involved in various chemical reactions. Using laser-induced diffraction analyzer Malvern Mastersizer 2000, we have identified the distribution of diamond soot particles by sizes in the electrolyte immediately upon preparing the suspension and after 10 hold-up days. Using gravimetric method, we have studied the aggregate and sedimentation stabilities of the diamond soot suspension in citrate-based copper-coating electrolyte. Analyzing the precipitating diamond soot particles dependence upon time Q=f(t) has allowed us to find that the sedimentation stability is essentially affected by the process of aggregating the particles, the intensity of which increased with increasing the concentration of diamond soot. The highest aggregation and sedimentation stability was observed for the diamond soot suspension in citrate-based copper-coating electrolyte with the concentration of 0.2 g/l. At the diamond soot concentration of 0.5 g/l or higher, the aggregation stability reduction was observed in citrate-based copper-coating electrolyte. It is found that, if the content of diamond soot in the solution is 1.0 g/l, the disperse phase is sufficient for the satisfactory sedimentation stability, which has allowed us to obtain copper coatings of low porosity and enhanced durability, as compared to copper coatings without adding diamond soot.