MX80 bentonite pellet/powder mixture has been considered as a candidate sealing/filling material in geological high-level radioactive waste disposal. As a single pellet can play an important role in the global hydro-mechanical behaviour of the mixture, the compression behaviour of a single MX80 pellet was investigated by performing uniaxial compression tests on cylinder-shaped pellets at different initial suctions, imposed by the vapour equilibrium technique. Large cracks were observed at suctions ≤ 9 MPa. Results from the compression tests showed that the axial strain ε axial contributed to the contractancy, whereas the lateral strain ε lateral contributed to the dilatancy. The uniaxial shear strength σ a, max , the crack closure (CC) stress σ cc , the crack initiation (CI) stress σ ci , the crack damage (CD) stress σ cd and the Young's modulus E were found to decrease with decreasing suction, providing evidence of the suction effect through softening and cracking. CI was considered as the inflection point of Δε lateral and the onset of dilatancy. Because of the combined effects of suction and wetting-induced cracks, the Poisson's ratios v increased until the suction decreased to 38–25 MPa, and then decreased with further suction decrease. Loading closed the wetting-induced horizontal cracks at suctions ≤ 9 MPa, leading to a drop of ε lateral before CC.