Abstract: Frictional characteristics of fretting rubber O-rings at low gas pressure were studied experimentally. The fretting frictional force between rubber O-rings and stainless steel 2Cr13 was measured. The experimental results show that O-rings frictional force had a hysteresis characteristic in the fretting cases. The frictional force had a linear increase with increasing displacement and became stable with increase of the reciprocating cycle number. However, the fretting frictional force varied significantly, larger than 30% in amplitude, with increase of the sealed pressure and the compression ratio.