Abstract: The experimental investigations on uniaxial compression of weakly cemented sandy mudstone samples under dry and natural conditions were conducted respectively to uncover the mechanical characteristics of weakly cemented sandy mudstone.The results indicate that compared with hard and brittle rocks, such rock has some characteristics including low crack density, weak self-stability; the course of volume dilatancy deformation is prolonged at the pre-peak; the delay effect and plastic flow trait can be showed in some stages at the post-peak; and the time of progressive failure is obviously short.The weakly cemented characteristics of such rock are primarily reflected in following three aspects:(1) the significant stress thresholds before the peak and the residual stress after the peak are obviously deteriorated; (2) the stiffness and anti-deformation of such rock are weak conspicuously; (3) the macroscopic failure characteristics of rock specimen are primarily result from three types of surface including tensile fracture surface, shear slip surface, and hoop shear failure surface, which have close relationship with some factors such as the crack progressive evolutionary characteristics, the density and the strength of bedding surfaces.(4) the mechanical characteristics of weakly cemented sandy mudstone in dry condition is similar to hard and brittle rocks, while the mechanical characteristics of such rock in natural condition are deteriorated in different degrees, including the important stress thresholds at pre-peak, elastic modulus, the residual stress at post-peak, and the degree of lateral expansion deformation is enhanced.It is essential to strengthen the initial support strength and consolidate strength timely to keep the tensile and shear failure in control and to enhance the rigidity and anti-deformation capability of surrounding rock masses.