Collective Thomson scattering has been applied to determine ion temperatures in the small-sized, low-density tokamak UNITOR with high spatial and temporal resolution. As the scatter light source a 400 kW D2O laser has been applied. The scatter signal are detected by means of a heterodyne technique. At an electron density of 3*1019 m-3 and an electron temperature of 180 eV the ion temperature reaches 20 eV+or-16 eV at 1 ms and 60 eV+or-25 eV at 2 ms after ignition. The measured ion data are confirmed by an energy balance.