The stab resistance of aramid fabrics reinforced with waterborne polyurethane (PU) resin is investigated by quasi-static and drop-tower stab tests. The effect of PU resin treatment and tumbling on the stab resistance is also evaluated by flexural stiffness and pull-out tests. To achieve maximum stab resistance, it is essential to control the movement of fiber bundles in the fabric structure. It is also found that the tumbling process is a useful way to improve the flexibility of treated fabrics.