A method of obtaining yttrium citrate by transformation of freshly precipitated yttrium hydroxide in the solutions of sodium citrate under hydrothermal conditions has been proposed. To determine the synthesis time, transformation kinetics consisted in by taking the solid samples for the C and H contents analysis after 6, 12, 24, 48 and 72 hours of synthesis. Simultaneously these samples were subjected to the thermogravimetric analysis. As follows from the thermogravimetric analysis adsorption of citrate dihydrate on yttrium hydroxide is observed in the initial period up to 24 hours. Later the yttrium citrate dihydrate is formed. The thermogravimetric analysis of the final product i.e. amorphous yttrium citrate showed that the decomposition/oxidation of the sample occurs in six stages the particle size analysis method of static light scattering showed that 45% of the particles had a diameter of 0.1-0.9m and 55% of particles with sizes from 0.9 to 5 um.