The friction performance of precision instrument-size ball bearings at cryogenic temperatures are special important in designing space instruments which are need to be cooled to low temperatures during operation. The friction characteristics of ball bearings can be obtained by measuring the friction heat generated by the bearings. A reliable method for measuring the friction heat in vacuum and at liquid helium (LHe) temperatures is proposed in this paper. The experimental results for a stainless steel ball bearing with different rotating speeds, axial pre-loads and temperatures are presented. The friction heat generated at the bearing sample is found to be proportional to both rotating speed and axial pre-load and to be independent of temperature in the test range.