Abstract: The creep behavior of rocks was investigated by many researchers.The time dependent behavior and strain-rate effect of elastic modulus were also studied by some authors.The lateral creep properties of rocks and deformation effect of elastic modulus of rocks,under creep condition however,were important for constitutive model and still have not been paid enough attention.In this paper,the lateral creep properties and strain effect of modulus under creep condition were experimentally studied using specimens made of red sandstone rock under step load with the developed gravitation style rock creep test machine.The test results showed that the lateral stress threshold of the second period was less than that of the axial stress threshold,the third period of lateral creep was obvious but not for axial one.The turning point of the third period of lateral creep appeared earlier than that of axial creep.Due to creep deformation,the instantaneous elastic modulus and the Poisson’s ratio increased obviously with deformation.