Abstract: It is more realistic that the clay unit cell of road embankment is in the state of plane strain. The creep characteristics of over-consolidated soils are studied through plane strain tests for the undisturbed soft clay. Four creep tests are carried out by using the plane strain creep apparatus, one is conducted on normally consolidated clay and three are on over-consolidated clay. The studies show that for the normally consolidated soils, the volumetric strain of creep in plane strain tests varies in the same way with the secondary consolidation under one-dimension condition, and that the clay presents less axial strain in plane strain tests than that in one-dimension tests when the principal stress ratio equals the ratio in K₀ state. The definition of plane strain over-consolidation ratio (OCR_p) is given, and it is used to describe the characteristics of over-consolidated soils. It is found that it is reasonable to determine the volumetric creep coefficient as well as axial creep coefficient directly by using OCR_p. Compared with normally consolidated clay, under plane strain state, the over-consolidated clay has a lager Poisson's ratio and larger principal stress in the direction of limited deformation.