The thermal structure of night-time plasmasphere is examined on the basis of some results of measurements of the distribution of concentration np and temperatures Tp of cold plasma in the Earth's plasmasphere. The results were obtained aboard the SA «Interball-2» («Auroral probe») in September 1996 and the satellite «Magion-5» in December 2001. It is found that nighttime temperatures, unlike day-time ones, strongly depend on the geomagnetic activity level: the values of temperature and, possibly, its height gradient diminish with increasing the activity. In quiet geomagnetic conditions the increase of Т_р with increasing height (or L-parameter) was observed regularly. For example, at a height of 5000 km 1600 < Т_р  < 2800 К and at a height of 10000 km 3000 < Т_р  < 4600 K. In this range of heights, middle gradient of temperature is 0.3 K/km for geomagnetic latitude -4° < λ  < 40°. Increase of Т_р in peripheral part of plasmasphere and in plasmapause, obviously, is related to intrusion of streams of keV-particles from magnetosphere to plasmasphere. Some experimental data on variations of distribution of Т_р (L) in night-time plasmasphere are given: before the beginning of the storm of 26 September 1996, during the main phase and in the phase of renovation. The reasons of the variations are discussed with allowance made for the corotation of cold plasma in the Earth's power tubes. Large-scale region with the negative gradient of temperature on L > 2, which was regularly observed by the SA «Auroral probe» in the day-time sector of plasmasphere during the period close to the minimum of solar cycle, was not detected in the night-time sector in September 1996. However, in 1999–2001 the region with the negative gradient of temperature in the night-time sector was observed by the satellite «Magion-5» once or twice.