Very limited research has been carried out to investigate sediment erosion caused by subaqueous inclined water jets, despite the fact that such water jets are used in subsea engineering (e.g., dredging, trenching, and deep sea mining). Therefore, we conducted a set of novel small-scale experiments to primarily study the effect of jetting inclination on cohesive sediment erosion. The experimental results reveal that vertical jetting results in the largest cavity depth (or ’erosion depth’), but not in the largest cavity size (sediment production). The erosion depth increases with the jetting angle reaching its maximum at 90° and then begins to decrease with further increase in the jetting angle. The results also indicate that the cavity width (or ’erosion width’) is not necessarily correlated with the impingement region but is instead associated with the erosion-effective jet width—the width of the jet where flow velocities are high enough to penetrate the bed. Analysis of the cavity size showed that the largest sediment production was achieved at a 65° jetting angle among the tested jetting angles (25°, 45°, 65°, 90°, 115°, 135°, and 155°). The erosion depth was found to be highly proportional to the impingement force exerted by the flow on the clay.