This paper presents a laboratory investigation into the undrained monotonic and cyclic response of weakly cemented sands. To this end, undrained monotonic compression and cyclic triaxial tests were performed on a clean sand, with cement contents ranging from 1% to 8% by weight of dry soil. The test results show that cementation has a significant effect on both monotonic and cyclic behaviour. At a given density and effective confining stress, increasing cementation results in the increase of both the monotonic undrained shear strength and cyclic resistance, as well as the transition of soil behaviour from contractive to a more dilative one.