Due to the scarcity of basic data of hydrate-bearing sediments, a series of triaxial tests are made on synthetic samples of methane-hydrate-bearing and tetrahydrofuran-hydrate-bearing sandy sediments, which are generated using the gas-filtration method and the pre-freezing method, respectively. Attention is focused on the bulk strength of the specimens at different levels of hydrate saturation. The contribution attributed to the back pressure is confirmed by use of the experimental data. The results indicate that the cohesion exponentially increases with the increase of the hydrate saturation. No significant variation is found in the internal frictional angle of the specimens with low to medium hydrate saturation (<50%), while the angle decreases with the increase of the hydrate saturation due to less particle interlocking at high saturation (>80%). In addition, the back pressure helps to strengthen the hydrate in voids and thus causes an increase in the strength of the hydrate-bearing specimens.