The current state of the research activities of the Main Astronomical Observatory of the NAS of Ukraine (MAO) in using the GNSS technology is presented. Today MAO supports the permanent GNSS network that consists of five stations (two stations are temporarily inactive). All stations are included in EPN and the EPOS network, GLSV, KHAR, and UZHL stations are also integrated to the IGS network. MAO Operational Centre also provides automatic operation of 12 stations installed by the another Ukrainian organizations, that are included to the international networks. Data from approximately 300 Ukrainian permanent GNSS stations are stored in the MAO Local Data Centre. MAO Local Analysis Centre uses the Bernese GNSS Software for different types of GNSS observational data processing. The rapid processing is performed on daily basis for the monitoring of stability of the permanent stations from some Ukrainian RTK networks. All available observations data from the Ukrainian stations for the period from December 7, 1997 to January 28, 2017 were processed according EPN standards during the MAO second reprocessing campaign and regular processing. As result, the coordinates in the IGb08 reference frame and troposheric zenith delays for 233 permanent stations (202 of them are the Ukrainian stations) as well as the velocities for the 128 stations that have observaion periods more than three years were estimated. The creation and development of local GNSS networks, as well as the long-term filling of databases with high-precision coordinate solutions and estimates of the displacement speeds of GNSS stations, made it possible to conduct geodynamic studies at the local level. Using the estimated coordinates and velocities of the GNSS stations the strain ellipses and rotation were found. In 2016–2019 Kharkiv National University of Radio Electronics in cooperation with MAO NAS of Ukraine has performed a number of studies for the purpose of high precision GNSS positioning and navigation. New implementations of modern methods and algorithms for the PPP positioning of ground objects were created and experimentally tested. The errors of the daily float PPP solutions are ~5...8 mm (with a probability of P ≈95%) for static mode and ~5...8 cm (P ≈68%) for kinematic mode. The decimeter/centimeter uncertainty of determining the current LEO satellites’ coordinates when implementing the kinematic float and fixed PPP solutions is proved. The development of a high-accuracy multi-position phase system of trajectory measurements for carrying out a range field tests of highly dynamic flying vehicles (HDFV) were proposed. The estimated values of the RMS errors in the determination of the HDFV motion parameters are in the limits 0.05 to 0.40 m for coordinates and ~0.5 to 1.6 cm/s for the velocity vector components.